Currently I'm using immediate mode for everything, all are rendered quads in my game. Since I'm in 2D ortho mode, the most quads I will ever draw will be about 5,000 on the scene at once. I'm undecided if I should go ahead and switch everything into Display Lists or VBO's, and switch all my particles into point sprites. For instance, your normal scene during game play you will see about 100 quads. 100 quads is nothing, and it won't make any difference what method im using to draw them. I'm just wondering if I should take the time to do this, when the performance difference won't be seen unless someone is trying to play on a 500mhz computer :/. The only calls I make are pretty much transform and rotate. And sometimes a glscale (zooming or explosions etc). and are point sprites a good way to do explosions? (movement, scaling, rotating) Should I just do it, or am I wasting time?

I don't think you will get a performance boost if that is what you mean because 5000 quads means 20000 vertices, which is nothing at all for the GPU.
The advantage of using VBO or display list is that you make less functions calls so it reduces CPU usage.

Well, if you draw 5000 quads in a frame, you'd need 20000+ OGL calls. If you moved this to VBO you'd get some advantages:
- vertex data is stored in video memory, i.e. it doesn't have to be passed over the bus every frame if it doesn't change
- the vertex data is compiled already and thus can be reused (if it doesn't change)

As a side note, if your transformations don't change that often you could calculate the transformation matrix once and provide this to OGL instead of recalculating it every frame.