Since I'm an ideas guy, I'll present my ideas towards making the emu faster (whether or not they are implemented does not matter to me, I'm simply throwing out ideas in an attempt to contribute to community)....Here goes:

Create option to enable/disable transparency
Create option to disable 'individual' sound channels

Create option to enable 'smart skipping'

This option gives the illusion of having full speed. I think vampent use 'smart skipping' concept for their symbian emulators particularly 'vbag'. This makes the emulator skip a certain amount of frames whenever it reaches a point where game is slowed down. I'll make a quick psuedo code to provide an example of my understanding in this concept.

While rom is running
Wait 5 secs
Disable autoskip
Check current fps
If current fps is <= 50fps
Then autoskip = 5 frames

//process is repeated by rechecking the current fps and skipping frames to a certain convenience in order to create the illusion of a smoother gameplay. Honestly though this concept may be a bit far fetched since I have only heard users mention this concept, and not vampent themselves.

There is also the option of creating a recompiler as smoku did, as there is high possibility of improving/doubling performance, but one has to know the emu they're porting extremely well (as in inside and outside well) as This method may actually degrade performance....
For example I have p64 emulator on my comp, by default the emulator is set to 'cpu interpreter' which is quite slow, but when I enable 'cpu recompiler' option, its performance / speed is doubled (doesn't happen for all games though)

Also I think vampent may have actually set the certain layers of sprite to perform a certain way, not sure.