Both cameras are nice and somewhat better than my GH2, but neither has all the features I want, nor does either have any paradigm-changing improvements over my GH2 (for what I do).
E-M1 has over GH2 (I owned GH2 since Dec 2010, GH3 since Sept 2012 and now I have E-M1 since Sept 2013) for somebody who uses a camera for still photo :
1 ) IS (IBIS) - you use manual focus lenses, that might be useful
2 ) better Panasonic sensor (more DR, more mp, no AA) - albeit it is not a multiaspect sensor (so if you like 16:9 instead of 4:3 framing mp advantage is gone)
3 ) better & bigger EVF
4 ) body with many more direct controls & more customization for those (and metal body, weather resistant - GH2 feels more like a plastic toy)
5 ) better shutter, faster x-sync, EFCS (no shutter shock), small flash can be remote (optical) TTL flash control
6 ) arguably better OOC JPG - that's certainly a matter of a taste
7 ) PDAF on sensor for a better (albeit by no means pro dSLR level) AF tracking (if you use AF lenses at all)
8 ) tunable real time blinkies in EVF for clipping indication (might be tuned, if you don't mind UniWB colored EVF for raw clipping indication)
9 ) I certainly missed some
technically - GH2 vs E-M1 is no contest (albeit your paradigm seems to be just fine with GH1 either).