Vehicle sizes

[Raapys]

I'd like to hear others' opinion about how vehicle sizes 'should' work.

More specifically, ways to balance the ship sizes in such a way that it's not an achievement by itself to build really large ships with lots of guns on them; ways to keep the smaller sizes from becoming obsolete just by having a new size researched.

At the moment( stock/kwok) this is done by the defensive modifier and, to a very small degree, speed. However, I find this method doesn't really do much good for keeping the player from using the biggest ship, at least in my case.

How does one give the player a reason *not* to skip straight to the biggest ship he can get, and how does one have the player keep using those smaller size ships even late-game?

I've a few vague ideas, but nothing coherent as of yet. What I'm thinking is that size shouldn't be what really matters; the ship-task should be. How about completely dropping the rather linear and generic size-based system( ships would still get more tonnage with increased tech level, though) and instead go for specific-task ships? This would require ship- size/task limits on weapons and a few components to be made effective.

A couple of examples:
Scout, can mount light regular weapons, very fast.
Missile ship, can mount no non-PD regular weapons, only missiles.
Destroyer, standard combat vessel which mounts most regular weapons, perhaps supports fighter bay and smaller missiles.
Heavy-cruiser( or something), can mount the largest regular weapons, weak defense, slow, no missiles.

Etc...

The size and stats of the ships would be made according to their task, research would improve the specific ships by giving more speed, tonnage, perhaps better-placed armor slots and such, blabla. The only real all-purpose ship would be the destroyer, but it would become more of a support ship for the special purpose ships, having no special abilities on its own.

Any thoughts on this forced mix of ship classes and its consequences? More fun/interesting than the regular more-size-less-speed each level approach or not? Any other ideas?