I wouldn't say it's a marginal replacement Miden. You should have a look at the specs side by side. One major addition is the Krome has over 3 gigs (almost 4) dedicated to the ROM. That's considerably more than the M50. Even if the the multi-sample and drum-sample number count is still the same, that's 3.8 gigs dedicated to that sound set as opposed to 256 Mb's found on the M-50

The Krome has a complete redesign.., with a new color display (the units not a physical rehash of the M50). Poly is increased, and there are also some new additions to patch editing (such as twice the velocity zones in the patches - including the drum kits).

IMO it's a pretty good step up from the M50. Also don't forget the patch set is the EDS-X. The previous model was just EDS.