Here are two Forum threads in which we've discussed the various issues related to sails on models:
http://www.finescale.com/FSM/CS/forums/603719/ShowPost.aspx
http://www.finescale.com/FSM/CS/forums/564680/ShowPost.aspx
There are quite a few different opinions in those threads. Please take all of them in the context of the others, and draw your own conclusions.
If you do decide to fit a model of the Cutty Sark with sails, the first thing you need to do is get a clear understanding of what happens to the yards when the sails are set and furled. The Cutty Sark has double topsails and single topgallants on all three masts, and a skysail on the mainmast. The three lower yards (for the fore course, main course, and crojack) are fixed in their positions vertically. So are the three lower topsail yards. The upper topsail, topgallant, royal, and (in the case of the mainmast) skysail yards slide up and down the masts when the sails are set and furled. When the sails are furled (or removed) the upper topsail yards are lowered until they're a few feet above the lower topsail yards. (That configuration, with just a few feet separating the upper and lower topsail yards, is highly characteristic of the ship. It's quite clear in the various photos on the ship's website.) The topgallant, royal, and skysail yards also get lowered, until they're almost sitting on the collars of the stays immediately below them.
The Revell rigging instructions aren't bad - certainly in a different world from the disgraceful document that comes with the Heller Soleil Royal. Revell has changed them several times over the years. The original issue of the kit, back in 1959, had remarkably sophisticated rigging instructions. They advised the modeler to make the topsail halyards and sheets out of 36-link brass chain, and add jackstays made of piano wire to all the yards. (The yards have rows of little pegs molded on top of them. Those represent the jackstay eyebolts. Making the jackstays from wire is an excellent idea.) I built that kit for the first time when I was about twelve years old; I remember how excited I got when my father drove me downtown to the hobby shop to buy that chain. (Dad balked a little when he discovered I needed 12 feet of the stuff, at something like $1.25 per foot, but he coughed up the funds. Looking back on it, I realize what he was thinking: if John wasn't fooling around with ship models, he'd probably be doing something worse.) The more recent issues have simplifed the rigging quite a bit. If you want to know what the rigging of the ship actually looks like, you can do no better than the George Campbell plans I recommended earlier. I can't think of a better way to invest $15 in a ship modeling project.
I'm afraid the good old days when Revell was the leader in the field of plastic sailing ship kits are long gone. According to Dr. Graham's book on the history of the company, Revell hasn't issued a genuinely new sailing ship kit since 1977. (The last one was a nice little model of a Viking ship - in my opinion the best such kit ever.) The first Revell sailing ship, the 1/192-scale Constitution, appeared in 1956. Revell has, in other words, been out of the sailing ship field now for more than half of the company's existence. (Revell of Germany has issued a few new ones since 1977, but they're hard to find in the U.S. - and haven't received exactly ecstatic reviews.)
Producing a new plastic sailing ship kit is, in fact, extremely expensive. The actual plastic that gets squirted into the molds does indeed represent only a tiny percentage of the investment. But the tooling of steel molds costs vast amounts of money - especially molds for 2-foot-long hull halves. The design costs, even with the help of computers, are huge, and still more money goes toward things like instruction book artwork, packaging, and box art. When I was working in a hobby shop (quite a few years ago) the rule of thumb (according to the trade journals and the distributors' reps) was that a kit manufacturer figured on breaking even on a new kit if it sold 100,000 units. I suspect the number is a little lower than that nowadays; the retail prices of plastic kits have risen somewhat faster than inflation, and I think the profit margins for the manufacturers are a little higher. But apparently the people responsible have determined that plastic sailing ships just don't sell well enough to justify the investment.
The question, "why stick with old molds?" has an obvious answer. New molds are expensive. Old molds cost nothing. A quick look at the current Revell/Monogram catalog will show that (with the remarkable exception of those beautiful new 1/72 submarine kits, the 1/400 Queen Mary 2, and maybe one or two others) all the ship kits - sailing ships, modern warships, and modern merchantmen - are at least thirty years old. In pure business terms that makes sense. I remember reading an article in one of the trade journals in which a Revell executive enthused over the fact that the company's 1/535-scale Missouri was one of its best sellers - despite the fact that it was an older kit and didn't represent the state of the art. It was a big money maker because the company had long since gotten back the initial investment; apart from the few cents' worth of styrene and the paper and printing for the box and instructions, the kit represented pure profit. That kit was originally issued in 1954. Revell/Monogram is still selling it - with a retail price at least five times as much as the original. By the standards of 2006 the thing is a piece of junk - but people still buy it. So why should the company make anything better?
The American plastic kit manufacturers in general have virtually given up on sailing ships. The current Revell-Monogram catalog contains three: two Constitutions and the C.S.S. Alabama. All three are reissues of kits that are at least forty years old. The only other American firm currently selling plastic sailing ships is Lindberg. All of its kits are reissues of extremely old ones - either Lindberg's own originals or kits that were originally issued by the long-defunct Pyro Plastics. (Some of those kits in pretty new Lindberg boxes are well over fifty years old.) On the other side of the Atlantic, Airfix hasn't issued a genuinely new sailing ship since the early eighties, and the most recent Heller one, the 1/100 H.M.S. Victory, dates from about 1978. At about that time a Japanese company called Imai issued a series of sailing ship kits that were among the best ever. (The Imai 1/125 Cutty Sark, in my personal opinion, is a better kit than the big Revell one.) Imai went out of business after just a few years. (Some of them have reappeared lately under other labels - usually at outrageous prices.) These are bad times for plastic sailing ship enthusiasts. There aren't many of them; they subsist largely on kits they buy at flea markets and on E-bay.
I'm aware of one company that's currently showing at least a little interest in the field: the Russian manufacturer Zvezda. It recently issued a medieval Hanseatic cog on 1/72 scale. I haven't bought one yet (the price is pretty steep), but it's been getting excellent reviews and the pictures of it on the web look great. (That kit, incidentally, is one I would recommend to beginners. It's an extremely attractive vessel that would provide some experience with all sorts of skills - assembly, painting, wood-grain effects, sails, spars, and rigging - without the amount of repetition that's inherent in a three-masted ship. A few weeks' work on that kit would be like an introductory course in ship modeling - and would produce a mighty handsome mantle decoration as part of the bargain.) I'll be extremely interested to see how that kit does. If it sells reasonably well, maybe Zvezda will consider giving us some more sailing ships - and maybe other manufacturers will follow the lead. But I'm not holding my breath in anticipation.