a few things:
– we don’t have a 64-bit kernel yet. if/when that arrives, there may be some further gains.
– for almost-there cases it’s good. eg, on the pi2 PS1 in enhanced mode (2x resolution), had just enough slowdown to make it not worth it, but is now perfect on the 3. there are a number of mame games that i’ve tried that are now perfect, and weren’t before. 32x, and certain snes games – all perfect now. mario kart 64 and f-zero 64 had small amounts of slowdown in 4 player on the pi2, so i hope that they’re perfect/near perfect on the 3 (with the right plugin).
– n64, dreamcast, etc – i’m not sure these emulators are mature enough to be perfect on any amount of power – all have graphical glitches on the cores we use, and huge system demands for the more accurate ones available on PC.
– i don’t know if i’d say it’s ‘worth it’ – i think these things are so cheap and i like tinkering with them as much as playing games on them, so it’s a new thing to play with 🙂