It's hard to tell without hearing it myself, but it's possible. The most recent unit I worked on that had intermittent snap-crackle-popping was actually due to a bad capacitor on its way out, there are a couple things it could potentially be. Changing the tube isn't super fun to do, but it's possible if you're handy with a soldering iron and comfortable taking things apart. The tube in most of them is 6N21B, unless it's a REALLY old one in which case it's a 6N17B-VR. Is there a version number printed on the circuit board?
That would be cool, and something similar could be done but not exactly that. A tube has 2 gain stages available; UA uses 2 and DW uses 3, so either way I'm sharing at least one stage. This would mean I could add a boost-type stage to DW for some cascaded gain action, but directly doing UA into DW wouldn't be possible without adding a third tube to the pedal.