I can't claim to be as familiar with Imai as some other folks. When the company was in its brief heyday I was working as a museum curator with an extremely limited income; I saw the boxes of most of the Imai kits (I think) in the hobby shop, but didn't have either the money to buy them or the time to build them.
Nor do I have a comprehensive list of them. (I think either Millard or Epinniger does; maybe they'll see this post and offer a contribution.) My recollection, though, is that the range in fact offered quite a mix of popular and more obscure subjects. Imai made a Constitution, United States, Santa Maria, Mayflower, Golden Hind, and Cutty Sark, as well as a generic (but quite believable) Spanish galleon and two galleys - Greek and Roman. (The latter two had some big problems regarding accuracy, but were nice pieces of mold-making.) The Imai 1/200 U.S.C.G.C. Eagle was, to my knowledge, the only Eagle kit ever put on the market that got her hull proportions right. (All the others were, I'm fairly certain, based on Harold Underhill's plans, which in fact represent the Gorch Fock - which was about 20 feet shorter.) The two enormous Japanese sail training ships presumably were intended to be popular subjects in Japan; I imagine they picked the U.S.S. Susquehanna for the same reason. Why they picked the Napoleon I don't know; maybe they were trying to tap into the French market, which previously had been thoroughly dominated by Heller. The chebec and the galleass probably looked like the sort of subject that a ship modeler who'd already cut his teeth on the more popular subjects would find attractive. And the range of nice little 1/350 sail training ships was timed to coincide with the much ballyhooed "Tall Ships Race" of 1976, which got millions of people (in the U.S., at least) interested (briefly) in such vessels. (It also seems to have inserted the dumb phrase "tall ship" into the popular vocabulary. Would that it could somehow be removed.)
Heaven forbid that I should pose as an expert on how to market sailing ship kits. But that actually seems to me like quite a good, comprehensive mix of the hackneyed and the less familiar.
Dr. Graham's recent book on the history of Monogram Models contains a faint hint of what might, I suspect, have been one reason for Imai's short life span. Imai leased some of its sailing ship molds (the Constitution, the United States, and maybe the Cutty Sark) to Monogram for a brief period, and Monogram marketed those kits in the U.S. According to Dr. Graham, the steel used to make the molds was so soft that they got damaged, and Monogram had to pay to have them "repaired" (whatever that might mean in this context) before sending them back to Japan. I wonder if some of Imai's molds simply wore out, and perhaps the company couldn't afford to repair or replace them. Dr. Graham's book doesn't say any more about that point. Quite a few of the old Imai kits are currently being sold under other labels (Academy and Aoshima certainly, and maybe others). It would be interesting to compare those reissued kits with the originals - and look for evidence of mold damage.
Imai also tended to go off on odd tangents. I remember looking at the Imai H.M.S. Victory, which was designed about like a plastic kit but had hull halves cast in white metal and spars made from wood. It was utterly awful - and expensive. I can't imagine that many people bought it, and it probably required quite an investment. I think I've also read about Imai wood kits, which I haven't seen.
The bottom line seems to be that this was an extremely adventurous company, with designers who were true artisans and a desire to make genuinely high-quality products. I miss Imai.
Maybe the biggest factor in the company's demise was the obvious one: it put a great deal of its money and effort into plastic sailing ship kits, at a time when that genre of the hobby was just about dead. At the present time it seems to be on life support. Revell (the U.S. company, as distinct from Revell Europe) hasn't issued a genuinely new sailing ship kit since 1977. (That was thirty years ago. The company issued its first sailing ship in 1956. Revell has, in other words, been out of the sailing ship business 50 percent longer than it was in it.) Heller and Airfix are out of business. (There are reports that Hornby is going to market at least some of the Airfix kits; I wonder if that will include any of the sailing ships - and whether Hornby will sell any of the Heller ones.) Imai is dead - except for some reissues under other labels, generally at sky-high prices. Pyro is long gone; a few of its old kits are being sold under the Lindberg label, which does seem to have gotten a new lease on life under new ownership. For a while I had some hope for the Russian company Zvezda, whose Hanseatic cog struck me as a fine idea for a plastic kit. But Zvezda hasn't shown much initiative since.
Frankly I've been pleasantly surprised at the number of folks in this Forum who are interested in sailing ships. The unfortunate fact remains, though, that we're in a tiny minority - and for the present it looks like we're doomed to survive on what can be found on E-bay at swap meets, and in the dark, dusty corners of the few remaining local hobby shops.
Or take the route I did: take a deep breath, swallow your inhibitions, and build from scratch. It really isn't as difficult as some people think - and scratch building opens up an unlimited range of subjects.