So I purchased an M3DS (homebrew card) in order to play some roguelikes on my DS. I'm still waiting for the SD memory, though…

Apparently, model quantity doesn't make much difference at ALL in terms of game speed. The completed ship (with destruction animation rig) is 1255 polygons; the following image shows 16 ships on screen at once (20k polygons), along with normal-mapped water and full reflection (partly obscured by the not-yet-perfect normal mapping). With one ship, game speed is 90-95fps.

As my plan for the game involves 5-ship-capped fleets (up to 10 ships in a battle) and modeled islands probably consisting of less than 5000 polygons, this is a Very Good Thing (TM). Even in the most hypothetically demanding situation I can think of, the game should still hit 30fps on most modern computers. (That's including game processing, ostensibly the slowest part of the whole affair)