I currently have the RS50 and have owned the RS1. If you know that the RS50 has decent to good convergence and a lens that is showing well defined pixels over the entire screen surface, it should be a sharper picture for you. It has an on board CMS which has some quirks about it but an experienced calibrator with good gear should be able to get much
better color accuracy than with your RS1. You may even be able to playing by yourself get to more decent and not as oversaturated colors as the RS1 has.
Motion is better for sports and I like to use the CMD (clear motion drive frame interpolation) on either Mode 3 or 4 with them. Seems to help motion some more to me and also give a bit more roundness to players and shapes. Just my feeling with it. With a Darblet a good RS50 can look really
If your RS1 has bright corners as mine did chances are you will not have any with the RS50, or they will be very faint if there at all. It's capable of (much?) better black level and contrast in your light controlled room. If the price is attractive you likely would consider it quite an upgrade with the quality of the picture overall.
Though prone to ghosting on difficult titles, movies such as Avatar and other CGI blockbusters with a new lamp can look really
good with 3D or in 2D with the Darblet. Although you would be better served with at that size a high power screen. If 3D not important don't sweat it.
Downside is this was the first year after the RS20 and following year RS25 with the not centered lens arrangements, where they went back to the lens in the center and you must have read by now a new series of very crappy lamps that most of them are at half brightness by 400 or so hours and often outright super dimming and failure shortly thereafter. They have gone through several batches of those (China) with no improvement, but possibly
the lamp now being supplied
with this little flap or fin thingy in the case that is visible may
be an improvement. But even with a brand new lamp it has less lumens than what you had with a new lamp with your RS1. Once the lamp is past a hundred hours or so most people can't get enough light for 3D without the high gain screens. If you have a long throw with your zoom lens you are going to lose even more of that light from the get go.
Hope this helps.....good luck with your decision.