MJH wrote: "Fair comment as regards the Heller Victory but do you think there are any ship kits that may have been so influential?"
Sure! The aforementioned Revell Missouri and the warships that Revell issued over the next year (Fletcher-class destroyer, Midway-class carrier, Baltimore-class heavy cruiser, PT boat, and the Nautilus) pretty much established what modelers expected plastic warship models to look like - how big they should be, how much detail they ought to have, and how much they ought to cost. Lindberg, Aurora, Renwal, and other companies jumped on the bandwagon. (A bit of research would be necessary to establish just how all this worked. I'm not sure, for instance, exactly when Lindberg's old Essex-class carrier was initially released. It may have beaten some of those Revell kits.)
In the area of sailing ships - I certainly agree with Jake about the importance of the Revell Constitution and Cutty Sark in terms of the influence they've had on consumers. On the other hand, it's easy to forget nowadays just how small the range of available sailing ship kits of that size ever was. Revell actually only made three that were honest-to-goodness different scale models - and released them over the short span of six years: the Cutty Sark (1959), Kearsarge (1961), and Constitution (1965). All the other big Revell sailing ships (Thermopylae, Pedro Nunes, Alabama, and United States) were modified reissues of those three. Heller made two that belong in the same category (and, I imagine, were heavily influenced by the Revell competition): the Soleil Royal and Victory. (Maybe the Reale and Chebec ought to be counted there too; I don't remember just how they compared in terms of dimensions, box size, and price.) Those big Revell sailing ships dominated the market, in a sense, for decades. When the Revell Cutty Sark was initially released it cost $10.00, and was, I believe, the most expensive plastic kit on the U.S. market. It was the sort of thing that adult modelers bought and kids (like me) dreamed of getting for Christmas. But the truth of the matter is that, in terms of the size of the range of releases, great big plastic sailing ship kits never really caught on.
In terms of influence on the sailing ship kit market, I'd nominate the original, 1/192 Revell Constitution. Originally released in 1956 (and still on the market), it did set a pattern: good historical accuracy, better detail than the solid-hull wood kits that made up the competition (dig those little tiny full-length guns sticking out of the ports!), a handy size (about 18" long) to go on the mantle, and a price ($3.00 originally, if I remember right) that wouldn't break the bank (and was far lower than the wood competition). It also introduced (I'm pretty sure) an alleged solution to the Great Ratline Problem: plastic-coated thread "pre-formed ratlines." Revell followed it up later that same year with its H.M.S. Bounty, and thereby set another standard: a series of kits on varying scales, adjusted to fit a standard-sized box. (To be fair, Revell was already doing something similar with its aircraft kits.) In 1957 came the Revell Santa Maria, which (I think) introduced another dubious innovation: the vac-formed "sail." The Revell fleet of sailing ships in those standard boxes grew to dominate the sailing ship market (at least in the U.S.) for at least twenty years. Several other companies adopted the vac-formed sail; I think Airfix was the only other one that offered pre-formed, plastic-coated "shrouds and ratlines." (Frankly I'm not sure either of those ideas was a good one, but there's no getting around their popularity.)
I'm a little nervous about asserting that Revell was the first in all those respects. Pyro, ITC, Marx, Aurora, and Airfix were also producing sailing ships in the mid-fifties; it's possible that one of them offered a kit with vac-formed sails, for example, before Revell's first one in 1957. (I have more precise info about Revell than any other company, thanks to Dr. Graham's book. None of this is original to me.)
I should also emphasize that my own personal experience with this stuff is almost entirely confined to the American side of the hobby - and in the grand scheme of things that's not fair. Airfix, for instance, was getting into the twentieth-century warship business at about the same time Revell was. I don't know exactly when the first Airfix warship kit appeared; I think in the late fifties or very early sixties, but I'm not sure. (Was it the Hood? The Nelson? The Bismarck? There's a book about the history of Airfix; does anybody out there have a copy?) Airfix probably deserves credit for establishing the "constant scale" principle; all its modern warships (and liners) from the beginning were on 1/600.
This is a fun, interesting topic. The more I think about it, the harder it is to narrow the list to just three kits. If I absolutely had to do that, I guess my choices would all be from Revell: 1/535 Missouri, 1/192 Constitution, and 1/96 Cutty Sark. But I'd expect plenty of arguments.