Grant, you're sure to have such a good time! I apologize for sounding preachy about the drinking issue; it just touched a nerve because during each of my four trips to Spain, I felt SO embarrassed to see groups of American college kids making idiots of themselves. They were often really (inappropriately) loud, sloppy/messy, and full of rude comments about Spanish food/customs/people.
On several occasions I heard drunken groups loudly criticizing Spanish people within earshot of MANY Spaniards, some of whom were bound to understand English. I felt it was incredibly insensitive and rude of the Americans to behave that way, and I imagine they would have been a little more circumspect about "sharing their feelings" if they hadn't been drunk.
Americans have such a bad reputation as travelers in many other countries--for not trying to learn the language, for being loud and rude, for dressing badly (maybe some of us deserve that part--you should see my dad when he travels in his white sneakers, khaki pants, and blue socks), etc. I always try hard to be the "perfect" traveler--friendly, kind, courteous, gentle, etc., and I get really upset to see people whose behavior just perpetuates the stereotypes.
That said, nearly everyone overindulges from time to time, and that may just be part of growing up--or growing up in our culture, where (as you point out) alcohol is certainly a forbidden fruit. My parents were like yours, Grant--if we wanted to drink wine or beer with meals, that was fine.
I guess the bigger part of my preachy advice is this--don't fall into the pattern of hanging out with Americans because it's easier to communicate. Make that initial effort, despite feeling awkward about the language, because you'll see a side of Spain you'll never encounter with crowds of Americans!
And regarding beer, you'll want to ask for a caña, not a cerveza, and probably most of the time you'll have to take whatever is on tap. It's all good. Maybe another difference in drinking styles (pointed out above, too, I think) is that many Americans don't think of getting tapas with each drink--having something to nibble on will keep you a bit more sober! Plus, some of the tapas are SO good and go really well with a glass of beer. Patatas bravas...mmmmm!!!!