That said: yes, the MakerBot really is just a refined RepRap. There's not much really of unique value there, technologically, beyond the aforementioned high expense of "refining" a hardware product.
Also they had a $10M round just recently, so those investors are going to want to cash out.
After that, theres rumors that their last year broke $70M in revenues (after $10M in revenues the year before), and they're not really slowing down.
So, all things considered its a high price, but I dont think $200M cash isn't too much to fork over.
The big question will be how they handle it. Will they start persuing all the other (much smaller) 3D printing companies for infringement? Will they just give makerbot more resources and freedom and tell them to keep doing their thing? Will they make their (professional) CAD software compatible with Makerbots printers and software, allowing a clean upgrade path between low-end and high-end printers? We'll see, but apparently Stratasys has high hopes for what they can do with it.
Also, the MakerBot Replicator 2, which has sold more units than all previous models combined, is mostly not at all opensource.
If $400,000,000 (possibly $600,000,000) isn't a big enough budget to develop a low end 3D printer, what are the development budgets of their industrial grade printers?