I'm sorry I've left my comments page neglected for a while, just letting everyone know that I've already picked songs for SCGMD3 so no need to leave more suggestions (in truth I picked them quite a while back, should've posted this sooner).
I plan on finishing the game over Easter since I'll have plenty of free time, but don't expect the same leap from 2 to 3 as there was from 1 to 2, it's mostly just some new songs to play. The fact that it's taken so long shows how little time I've found to actually work on the game, so revolutionising it isn't really feasible.
Thanks for the support guys!