When playing $1-$2 NL live, many players do not 3-bet very frequently pre-flop. Although important in theory, I rarely do so with less than QQ. Is this likely to be exploited at this level, or is it fairly safe not to worry about it due to the slower pace of live play (and the lack of tracking software)?
Players at $1-$2 NL live are generally loose, so you should definitely widen your 3-betting range to, at the very least, JJ+ and AQ+, especially when in position.
Of course, all players and games are different, and you should adapt to your opponents' particular tendencies.
The answer to this question is very situation dependent. In general, you need to look at what opponents will call with.
If you are at a table full of nits, you can take down more pots pre-flop with a wider 3 bet range, but you will be risking a decent amount for likely smaller pots, where it might be a better risk/reward proposition to apply pressure later in a hand.
If you are at a table with shortstacks that are calling a lot preflop, and you don't mind variance, you could widen your range to some better Ax hands and take some slight edge flips.
If you are at a very loose table that is calling with lots of suited, connected and weak broadway hands, you can widen your 3-betting range for value. You will need to be comfortable continuation betting, and a fairly skilled hand reader, for this to be profitable.