You basically do not need a tube guitar amp that is bigger than 50 watts. They're more than loud enough for small to medium stages, and if you ever play anything bigger than that the sound guy is gonna mic your amp anyway. Plus, 50W amps tend to sound a lot better than bigger amps because you get the sweet, sweet power amp distortion at lower volumes. One possible exception is something solid state or a Fender Twin, where you're going for as much clean headroom as possible. Also I've found that amps that use digital modeling technology are really power-hungry. When in doubt, go for higher wattage on those guys.
Right now I play a MESA/Boogie Nomad 55 4x10 combo, and it is literally too loud for my metal band if I turn it up more than halfway.
As for bass amps, more watts is always better. If I still played bass much my dream setup would probably be a 1000W power amp and a nice tube preamp, either an Ampeg or an Eden.