Friendly blackjack dealers - I’ve always liked the dealers at the Flamingo. They’re my favorite (of course, there’s always exceptions), but I’ve had fun at the Mirage and downtown at The Golden Nugget as well.
Loosest slots - According to the Wizard of Odds, the Palms has very loose slots for the Strip area (although the article linked to is from two years ago, so it may not still be true). Also, the Station casinos (Palace Station, Sunset Station, etc.). In general, from what I understand, the downtown casinos have higher payouts on their slots than on the strip.
Best buffets - for breakfast, definitely try the one at the Paris or at the Bellagio. For a little less money, but not of terribly less quality, the breakfast buffet at the Aladdin is very, very good.
Comps - What games do you play the most of? The best way to get comps is to stick to one casino, but that’s not as much fun, of course. Things are pretty lean in Vegas right now, due to the economy and the casinos not getting as many high rollers from Asia at the moment, so as a results, comps are harder to come by. If you’re betting less than $25 a hand, you’re probably not going to get anything. If you’re serious about getting comps, check out Comp City by Max Rubin, an in-depth book on getting comps.
Hoover Dam is definitely worth a day trip, but I would seriously consider Red Rock Canyon. It’s only 17 miles west of Vegas, and absolutely stunning.