Although you’re referring to the Mountain Buggy, I want to elaborate on your subject of adapters.
the BOB does not make adapters for many popular car seats, especially the better quality ones. I know BOB is such a household name, but when shopping for a BOB, that’s one thing to keep in mind.
If you’re using a stroller for casual street running, I don’t think you’ll need to spend the extra $100 on a Mountain Buggy, but if you’re a more serious runner going better than 7 min pace or running trails, there’s absolutely no substitute for a Mountain Buggy. If you have time to wait, the new Mountain Buggy will be out around March 2015 with a more aesthetic frame and one-handed fold.