Well, after playing both, I decided to just keep the speakers they way they are. I get great sounds out of both. I also was talking to some speaker oriented people, and they said that mixing speakers with different sized dust caps can make it hard to EQ the amp, as the dust cap really affects the high end. It'll sound good on one side, but not on the other.
The Maverick and the Tremoverb are quite a bit different in terms of voicing, and also just overall "gain". If you read the original Mesa Writeup, the Maverick is almost like two single channel amps put together. The two channels do not share any tube triodes until the effects loop, which really can help zero in on a sound with careful tube choices. The Class A EL84 output section also is quite a bit different, so the overall response is different as well. The Maverick also uses the 5AR4 rectifier, which is the "least saggy" of all the rectifiers that mesa uses, so honestly there is only a very subtle difference. With the tremoverb, you definitely get some serious tube sag from the 5U4G rectifiers.
If you like mostly low gain and clean playing, the Maverick is really a better choice. It's even got two clean modes, bright and fat, which further help dial in the sound. You can get some dirt on the Rhythm/Clean channel, but it's very smooth an subtle. The lead channel is much more of a classic smooth boogie gain sound. There are also only 3 gain stages on the channels, so they aren't capable of nearly as much saturation as the Tremoverb.
The Tremoverb is definitely more versatile, but it also can't get some of the territory that the maverick does in terms of low gain. The reverb on both is incredible. THe tremolo on the Tremoverb is... kinda gimmicky if you ask me. It's more subtle than most would like.
One thing to consider with the maverick is that it will require more frequent tube changes due to the Class A EL84 output SEction. It isn't as bad as some of the early Studio caliber amps, but they still do get run pretty hard.