Ignore them! Dropping 'e' and vomitting on the pavement isn 't compulsory for all visitors. This can be the most relaxing place on earth, and you need never hear a drum or a bass(?) for your entire stay!
I went on one of these to San An in 1989 with a friend who'd never been abroad. On the 1st night, the reps took us on a pub-crawl at 8.00pm (even then I never used to go out until 10.00) to the most expensive bars. At about 9.30, we left the crawl, and found....a locals bar! Speaking a bit of Spanish, we made instant friends (Bobby Charlton again), and drank stupidly large Bacardis for a comparative pittance. The next pub-crawl night, we took about 5 of the more reasonable people we'd met with us to the same bar, and the reps never spoke to me again!
The reps are on a kick-back from the tourist traps. These holidays are good value and great to meet other people, but you don't have to be a sheep. Don't feel compelled to drink at 10.30 on some stupid trip if you don't want it. In fact, don't be tempted to pay for all the trips in advance, no matter how much pressure the reps put on you!
Believe me, it's not worth the effort! If you want to go, take a bus and get there early before the crowds get there (at about 10.30). Then you can leave when you want, and walk down to Sargamassa for a swim - you'll need it!