I'm sorry but I don't see the point of having non-powered land vehicles (horse-drawn carts/carriages, bicycles, skateboards?) particularly with old horse-drawn carts, how would we identify a "make" for these? And no offence, but I honestly don't see the point in listing fictional spacecraft, at least I have no interest in this. The thing about IMCDB is someone can go "I like this car, which films does it appear in?" With fictional spacecraft, everyone knows that the X-Wings and TIE Fighters appear in Star Wars films, the Enterprise appears in Star Trek films, Nostromo appears in Alien, Firefly appears in Firefly and Serenity and so on. And these don't even exist as actual vehicles, they are only models or CGI. At least with made for movie cars, most of them actually work as a powered vehicle. This is why I don't believe in listing models of fictional land vehicles, like in the film Dune. You could use this argument against cartoon cars, but I feel it's OK as long as they closely resemble a real car (stuff that is too generic and vague to identify as a rendering of one exact vehicle isn't worth listing IMHO).

An IMVDb is a nice idea (if we restrict it to cars, trains, sea-going vessels and aircraft), but it sounds difficult to find a way of listing them all together in each film. Would it simpler to create one site for aircraft, one for trains and one for boats/ships, and keep each mode of transport segregated to these sites? I suppose it depends what people are interested in, I'd like to see a site for aircraft, but I'm not really interested in trains (but that's just me).