A
tube power amp will completely change your tone, but most likely in a good way. I like the 2/50/2 because it is a little lower wattage and you can really get the transformer singing. If youre running the local club circuit (as most of us are) I dont think Id walk in with anything more than 100 watts because it is harder to hit the
power amps sweet spot and really get the tubes interacting with the speakers if you have a soundman constantly telling you that youre redlining his board (trust me on this one). The EL34s are going to give a bit more of a Brit sound (but then again...Vai uses EL34s

) so you may want to research different types of power tubes to select the sound youre looking for.
www.amptone.com is a great reference as is the sticky post on tube selection at the top of this section of the forum (I recommend checking there first!). The only problem that *I* can foresee (and Im by no means an expert on digital modelling) is that the cabinet emulation functions of the POD are going to be colored by the power amp (if indeed you use them in a live situation).