Interesting points about different weapon types. In my game the player's ship will primarily be attacking with a single, upgradeable turret, plus "smart" missiles.

How does your game handle switching between different weapons types (or does it?)

I'm currently leaning to having equipment upgrades + modifiers. So the player upgrades armor along a single path, but can purchase or find special artifacts that give bonuses, like 10% damage reduction, etc, 20pt damage thresshold, etc.

Regarding performance, so far I'm not really hitting any bottlenecks in terms of the actual game mechanics. The player's FlakController (defensive fire) averages ony 0.04ms per frame. For comparison, updating enemies is about 0.1 ms per enemy per frame.

What does hurt are sounds (8 ms per sound.play call) and graphical effects, which can be adjusted to match the user's machine.