I'd rather they concentrate on making them shorter rather than loading a car model for us to manipulate.
I think "loading" shouldn't occur at all. The menu should just sit over the top of whatever you're doing in that moment, I don't understand why the game fills the RAM with a location and cars, then seems to proceed to dump all of that to load a menu again, only to have to dump all of that to load the next location etc.
Granted, the PS3 is crippled by its memory, but that only means the menus should involve less loading by design!
This is probably a nightmare for resource and game state tracking (particularly in freeing up allocated memory) etc., whilst the "traditional" method is great for providing a clean slate between races and for ensuring the game state is just-so, but games are going to get bigger and more complex and this loading problem is only going to get worse, so we need a solution sooner or later. Besides, it's almost idiotic that the game has to load the car you were just driving when you get back to the garage after a race...
The game is fully capable of streaming, it should allow you to mess about in the menus as it loads whatever it is you're off to do in the background. E.g. you pick a race and whilst it's "loading" you can tinker with your cars in the garage, or just do anything, including cancel the loading / load something else instead. Some indicator of how much bandwidth you're taking away from "loading" your race to do that fiddling about would be helpful, too, so you can choose to take a hit to loading times in order to be able to while away that time, or just sit tight and watch nothing happen, like we're already used to. All that said, there was one update that really chopped the loading times down and sort of provided this functionality already: it started only loading the part of the track that is first visible, then it brought in the race menu as before and loaded the rest of the bits of track needed (those nearby) and all the cars, allowing you to tweak your car whilst it loads.
Note that the game also already does the "look at this pretty car whilst we load something else for you" thing in the demonstration mode off the first / main screen, and that was one step up from what Prologue did, too. Why wasn't the whole game built on that foundation? We can only guess, but maybe that, and that loading update I described, actually shows promise for the future.
Why not have the museum feature play during loading times? Like, one random museum card could pop up and you have something interesting to read while waiting. Shouldn't take too long to load that.
Yep, it wouldn't take too long to load a small image (or a Standard car

) and a little bit of text, you could even make it fully browseable. If a system similar to what I described above gets implemented, maybe, if you've no tinkering to do, having the museum somewhere close to hand would be helpful.