I had my Helix for a year and a half and the possibilities with the Variax over VDI had intrigued me from almost the start. A month ago I bought my JTV-59, and while I'm still in the honeymoon period, I've been quite pleased with it so far.
The one major thing about it though, is just like the Helix, you need to do some tweaking and not be afraid to get your hands dirty in Workbench, which has its own learning curve. It's got some playability out of the box, but it really shines when you make it your own. When you couple it with the Helix, you get a lot of flexibility and options, and you can bend your sound around the modeling's shortcomings. There's a lot of places to get lost crafting a tone, but when you do, it's gold. While it's never THE exact guitar you're modeling, especially in terms of feel, it's close enough, and even closer in a mix.
I've yet to have any real issues with palm muting. Maybe my technique fits it well or something. The neck is FAT though, as some have said. I came from a PRS S2 Standard 24, and it's manageable for me, and I've got fat hands and short fingers. I've heard some complaints about the acoustic sounds, but they're quite good enough for me with a mic preamp and some reverb. You definitely need PA range for it though, the acoustic models sound like trash through a regular guitar amp, but then again so does any piezo acoustic.
Unfortunately I can't really speak for the resonator or banjo stuff, as that's not really in my style. I will say that I can get lost for DAYS messing around with the Coral Sitar model. I thickened mine up with some parallel pitch, fattened it by stacking a middle pickup on top the bridge pickup, and did something I can't recall to make the drones stand out. I'll crank it into drop d and before I know it, it's 2:30am and I'm still wailing away on it.