I don't think they are overrated but they have been putting out lower quality amps for a while, as well as higher end ones. I know 2 people who recently bought "Marshall" 1/2 stacks that were made in Viet Nam (I'm not making this up), solid state with built in multi-effects junk but these guys thought they had the real deal because it said Marshall on the front. I'm not slagging Marshall for making lower end products for beginners; just about every gear company is now, but I can see why some people may think Marshall is overrated depending on what they play through.
I have Marshall, Mesa Boogie, Tech 21 and Epi Valve Jr amps and they all fit their purposes well.

PS the Crate Power Block/POD idea sounds like a good, inexpensive and versatile rig.