A friend/old bandmate is selling a white Mesa 412 cab loaded with celestion v30s. Just needs to be wired and that's it. There are no casters with it, but that's not a huge deal I wouldn't guess. He offered it to me for $300. I don't really have a need for it (I have an evh 5150 iii 50w with an orange ppc212) but that's a great deal, which is why I'm considering it.

Is that a solid investment or should I pass on it since no real need (I don't gig or anything).
I'd personally skip it and save the money for a necessary upgrade. Your rig sounds like its fine to me, and an extra cab is just more to haul around. Plus I hate fixing things, but thats me.
I see a good resale profit here if you don't like it. The wiring cost is negligible and casters aren't much either.

I see the black ones go for $450 regularly, sometimes more depending on the shape and your patience.
Jackson Kelly KE3 - MIJ (Distortion/Jazz)
Jackson DKMGT Dinky (EMG 81/85)
ESP E-II Eclipse Custom (JB/'59)
ESP LTD EC-1001FR (EMG 81/60)
Fender MIM Strat

Mesa/Boogie Dual Rectifier Roadster 212
Laney IronHeart IRT-Studio
Peavey Vypyr 30
Peavey ReValver Amp Sims
TOOOO many T.C. Electronic Pedals. . .