A few reasons I bought one without ever seeing one...
I want to get this one calibrated eventually. Like previously mentioned, the VT has the widest array of adjustments for a calibrator.
I want to (hopefully) be able to be satisfied with this TV for longer than my last Panasonic. I figure buying "the best" would help with that and keep me from regretting and kicking myself for not spending the extra from the beginning. Two years ago I bought a G (non-3D since this was before the GT25 was ever announced) model, and while I loved it, always wondered what performance I was missing.
Another reason is that the VT is the only model with a 96Hz option for 24p material. I mainly watch blu-ray and while the Panasonics do a very good job set to 60Hz, I'd rather not have any 3:2 pulldown being done if I can avoid it. 48Hz on ST and GT also introduces too much flicker.
Lastly, the design. All the ST/GT/VT models got a nice design overhaul this year, but the VT50 looks like a big improvement over the clunky VT30. It looks like it retains the single sheet of glass while getting rid of the gigantic bezel from last year. It looks kinda like Sony's Monolithic design, which I love.