I just got my pi 3 yesterday and N64 runs slightly better, Dreamcast runs a lot better (I can play games like UFC that were unplayable on pi2) but still not perfect like psx. The most improved is the psp. I’m using the ppsspp emulator which gives you more options to bust down the graphics than lr-ppsspp. The graphics aren’t quite as sharp as the standard settings but games run perfectly smooth (better than N64).
So considering the performance bump already, and eventual safe overclocking, retropie being made to better suite 64bit, and the build in bluetooth/wifi it was totally worth it for me.