I've owned a GH1 since 2009 and bought a GH3 in October 2013. I can't comment on the GH2 in any meaningful way and I've just begun to push the GH3 to it's limits. I feel confident recommending a GH3 over a hacked GH2 for one reason: the GH3 does not require a hack to produce excellent results.
Besides providing a great image without requiring a hack the GH3 also offers improved ergonomics and physical connections like a headphone output and a normal 3.5mm stereo input.
Even though the wifi connection isn't a cakewalk it's immensely useful within it's limitations.
I paid $850 for my GH3. A used GH2 isn't that much cheaper and a new GH4 won't be that much more in a year.
In other words, don't sweat it.
Used GH2s are selling for about half that price.. for me it's big cost difference but not that giant leap in quality... Headphone out is usefull feature, but I can live without it and have 2 GH2s for price of one GH3 and with additional accessories (e.g. spare batts) maybe if GH3 had better sensor with higher DR and better highISO performance I'll buy it.. but it hasn't..
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