I'm not sure about this - certainly as far as the "not sufficiently well detailed" part goes. I firmly believe that if a manufacturer brings out a low-budget model of a previously unreleased prototype (e.g. Adelante, Class 800 or perhaps even something like a Gas Turbine), people who want a model of that particular loco/unit will still buy it, and the market will be opened up to people who couldn't afford a more expensive model.
The Bachmann Skarloey is a case in point - whilst clearly a toy model (albeit retailing at Peckett prices, largely due to the licensing fees - had it not been for that, I reckon it could have been obtainable for around the £50 mark) - as it's the only RTR model of a 'Talyllyn' style loco, importers in the UK have seen them flying off the shelves (one importer said his US wholesaler had sold him more than all his US retailers put together!). Likewise I'm sure that if Hornby were to bring out a better-proportioned 'Toby', anyone wanting a RTR J70 would buy it, irrespective of the lack of detail.
There are still a lot of unreleased industrial types out there, which would be well-suited to Junior layouts but which would probably sell well to anyone wanting a model of that particular class. If someone wanted say a Bagnall 0-4-0F, would the fact it was produced without sprung buffers or a fully-detailed cab interior really put them off buying it if the price was commensurate with that?
This may (or may not) also apply to prototypes which *have* previously been released by other manufacturers but are now unobtainable (e.g. Class 14).