I own a Sony R7, a D7, the very cool MUR201, and the big sampling verb (S777). I love the Sony boxes...great sounds, clean and clear. The MUR201 is a very cool kind of lo-fi true stereo verb, a little noisy, but really nice sounding (like a better sounding stereo REV7). I would not think of the MPX500 or 550 (both of which I've owned) as similar to the R7...but that's just me.
I really like the D7. Not as pristine as the 2290, but nice, and stereo (unlike the 2290). Cool tremolo effects, too.
The plates on the R7 are very nice...lonnnnnnng smooth tails for stuff that needs a shimmery kind of verb.
-tom