If you (a) have the spare money, and (b) are prepared to spend that money on an 060 or PPC and (c) if you can actually FIND a PPC board... then fine. MUI may or may not be good on those chips. Most people with Amigas seem to have 020 or 030 chips. Personally, whilst point (a) is not a problem, points (b) and (c) both receive negative answers. They are expensive and obsolete. You can't watch DVD movies on an 060, can they play flash movies or convert Mpeg/AVI movies at high speed? Nope! As for PPC boards... as rare as hen's teeth.
It's the same situation as Windows users have had for many years. Upgrade your processor and memory to run a newer, better O/S. At least in the IBM compatible world, processors are cheap! I may be upgrading my 030/50 to an 040/25 very soon, but only because I know somebody who is retiring their Amiga, complete with 040. MUI is unlikely to get a look in though.