There is more that should be changed about the particle system. Particles are great. A particle thruster won't show seams as bad as a static image does.
I'll pick up this example:
Thruster particles grow smaller to the end (either by code->smaller particles, or they'll just have to be smaller on the map). The problem is the particles spawn with 0 speed and at a fixed rate. So it works for the start very well. The particles overlap and look like one part, but they grow smaller to the end and gaps appear. The particles should just follow the ship with the same speed and get slower with the time.
That's it. We can add nice 3d thrusters as soon as this is possible.