Some of the dark overtones comes from the Mesa STR440's. I have tried other power tubes and have favored the SED = c= 6L6GC overall but it does add brightness to the amp. I would definitely give a TS in V1 and V2 a try, use the stock Mesa tubes for the remainder. That actually sounds really good. If you want more edge, install a Mullard CV4004 tube in V2, that will make a huge difference on the gain stack. What surprised me was a JAN/GE 5751 in V1 with the CV4004 in V2. Don't let the lower gain of the 5751 tube fool you, especially if it is a NOS tube. To me it was too much gain. I actually like the darker tone of the stock tubes.
V30's will flub out in the larger cabinet. They do not perform well in an open cab either (they do the same thing) However, they perform incredibly well in a standard sized 412 cabinet (the smaller one). Still there is the shift in tone though the V30 when compared to other speakers. Changing speakers may not always produce the results you may thing you will get. Definitely keep other alternatives open before changing speakers.
Blanket, that is how I felt about the Roadster though the V30 cab that I have. My RA100 and Mark IV sound great thought the V30's, the Mark V and Roadster sound like a blanket is on the speakers and pillows stuffed in the cab (yes I tried stuffing pillows in the cab to hear the difference in an attempt to eliminate some drone, actually made it worse since it was due to air movement and the ductwork under the floor, installing the casters was the fix, no pillows.) Actually my V30 cab is not all that bad if I dial in the amp for the cabinet.