[LOTF]

For the size of the gigs you say you're playing, I think 15 watts through a single Celestion Blue (e.g., AC15CCX) would be quite sufficient. If I had it to do over, that's what I'd buy. Fifteen watts of tube power is a lot louder than you might think it would be. If it isn't quite enough for the larger end of the scale, you can always mike the amp through the PA, which is what most people do for larger gigs anyway.

Both wattage and speakers are important. The sound comes from the speakers and two speakers indisputably move more air than one does. But the power needs to be there to drive them. If you run an AC15 through twin Marshall cabs loaded with 4x12s, it isn't going to sound the same as running a 100-watt Marshall head through those bad boys.

The other thing about speakers is tone. The reason real VOXheads prefer the Celestion Blues is the authentic tone. In fact, that speaker won't take as much power as the Wharfedales that come in the cheaper version (like I've got). Thus, though they'll start breaking up earlier, which is good, they'll also blow earlier, which most certainly isn't. If I ever decide to upgrade the speakers in my AC30, I'll most likely go for Celestion Vintage 30s, not the Blues. Furthermore, all these amps (or at least the AC30s) have a remote speaker output. If you find that a single speaker isn't enough for your sound, it's an easy enough matter to add a 1x12 cab to get that extra air moving.

Another thing to consider in the equation is the rectifier. The AC30 uses a GZ34 tube rectifier while the AC15 has a solid-state one. Tube rectification will improve your sound, no doubt. But you say you come from a "musically challenged" country and a GZ34 is not necessarily the easiest tube to obtain, even in places where such things are more readily available. If you have the misfortune to blow your GZ34 right before or during a gig, you'll be SOL unless you have a backup amp available. This isn't a worry with the AC15's solid-state rectifier. Just something else for you to consider.