I don't doubt at all that there is some difference in overall sound, smaller cab does in fact usually equal somewhat "smaller" sound. A 1x12 combo is never going to sound exactly like a full stack, now matter how good the combo is...and so yeah, to a lesser degree the 1x12 will never sound quite as full as the 2x12. But I do believe that all the actually components of the amp are the same, except of course for the power rating.
With regards to what I was saying about the wattage of the amp, is that so many times people want a "tube" amp and want a bazillion watts...LOL...But then end up playing with it set at about 2 most of the time. In that situation, having a "tube" amp is kind of pointless, since the tubes aren't really being pushed. Cranking a tube amp is where the "tubeness" of it really kicks in. That's partially why you're seeing so many really low watt, but high end/priced combo amps these days. Home recording is more popular than ever, and people want to be able to crank up a good tube amp when recording. But if that puppy is 100 watts, you're only cranking for a couple min, before the police show up. LOL Unless you've got an isolation room or something...but who has that? :D But...if it's a 5w/10w/15w/25w or so, then it's do able...usually.
Anyway...now that I've typed an entire novel again...It does just come down to the best blend of what sounds good to YOU and what you can afford. And definitely try out as much as you can before buying, if at all possible.
Best of luck,