Rare isn't Rare because of numerous staff changes that have gone on consistently since they left Nintendo. It has nothing to do with leaving Nintendo and going to Microsoft, but a lot of staff members have left since then. This article shows that Rare is continuing to dissolve and further and further.
They've dissolved to the point where it means nothing that MS bought them. You buy a company for the people that make the company great. You don't buy for the brand name "Rare."
If their most relevant title is Kinect Sports, from both a fan perspective and business persepctive then they aren't worth much. Kinect Sports has stagnated too much and hasn't even passed 3 million. If you need a killer app for a piece of hardware then you want to count on those big name companies like Rare. They didn't deliver(even on a Wii Sports Rip-off!) and MS still wants to make them the center piece for Kinect.
