gpSP's code is very old for me, and a lot of the code in DraStic is doing similar stuff but better, that makes it very hard to go back to it.. I was still trying to improve gpSP up to 2008 but found it impossible to make myself work on the code anymore.
From everything I've heard, other emulators on Android like MyBoy! have superseded gpSP in every way that matters. I don't know how they compare in terms of efficiency, if they're as fast (or faster). But it's fairly moot since few phones require that kind of performance for GBA emulation, they're not 200MHz ARM9s like GP2X. gpSP likely has worse compatibility and fewer features than most of them, not to mention pretty broken cheat support.
Also, I really have nothing to offer for an Android port of an open source emulator. I have zero experience with Android-specific code. In DraStic all of that is done by Lordus.