For Workbench type usage an '040, and an '060 even moreso offer a noticable upgrade from an '030. The incompatiblity issues with them are somewhat exagerated (never had a problem with my '040 despite it being constantly touted as least compatible cpu for amiga). Gaming wise, running original floppy disks can be a little hit and miss, but using whdload, again even with an '040 Ive had no issues. The difference with what you have now and an '060 is probably something akin to the difference between a stock a1200 and what you have now, definately noticable, and some nice benefits.
Just remember that the faster the cpu/ram, the greater the advantage of things like fblit will have, plus there's more room to add some extras without making noticable performance hits. It could be th difference between keeping things speedy using 16 and 64 colors (for a random example).
PPC I personally was disappointed with, and given the choice Id go for a faster 68k cpu and no ppc rather than a slower 68k cpu and ppc. Obviously both would be ideal if a person has the money to spend
