I've heard the M80s, M60s, VP150 and VP180 and also agree that VP180 over VP150 is a greater improvement than M80s over M60s.
If money is not an issue and you feel like upgrading than I would say now is the time. The M80s are a bit more detailed in the mids, aka even less forgiving to bad recordings than the M60s, and have a bit more bass.

Bruno
M80s/VP180/QS8s/EP600/AVR-890
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"The problem is choice..."