The Runco 50 is based on an NEC 50MP1 panel, with a Runco scaler bundled with it (hence the additional cost).
I'm not quite sure what, if anything, Runco does to the plasma's electronics, but the scaler sure makes the picture look good. However, in the various plasma reviews that have been done, the Fujitsu, Pioneer and Panasonic latest-generation models have fared slightly better. I've seen both a Runco 50 and 61 and they look very nice, but I've not seen them side-by-side against the other late model 50's.
My personal opinion, worth what you pay for it, is that you can do essentially the same by purchasing the plasma panel you like the best and matching it with a scaler you like, and with the discounts available on the Net for these components, you can achieve the same or better performance for less $$.
Cheers