I opted to vote for stuff that could be improved by adding some Hu power, given the original arrangement being strong, but the hardware implementation lacking teeth. This would cover pretty much any memorable SNES song that is not orchestral.
Starfox (great, but brought down by too much SNES)
Gaiares Mission 3 (I like the original, but feel it will be better in the PCE)
Mega Man X (not one of my favorite songs, but it is from one of my favorite games of all time. Would be interesting to hear it in the PCE)
Axelay (same as Starfox)
Super Monaco GP (awesome song, marred by poor instrument choice)