Check-raising when you flop the set is a bad idea against a preflop raiser. It's better to lead into the raiser in hope of being re-raised. Check-raising is to strong of a move and counterproductive when you flop a set.
Totally dont agree if you have already made this play with less. It isnt necessairly about the move, its about what you will make the move with.

Set hunting is less viable in tourneys then in cash games because the effective stacks are often not large enough to justify playing to hit a set. This lowers the value of low pocket pairs in tourneys.
Again dont agree. Get some post flop play. Harrington suggests pps are no good to ep raisers. Well who doesnt raise AQ in ep in an mtt? Fact is that if you start betting low flops and get folds but fold yourself to 3 bets then you know you arent good. You dont need to have a set to play big pots against ace high. Same applies to cash games, where too many people just hit the fold button without a set. Again, playing pots with more marginal but good hands increases stacks in mtts and bb/100 in cash games.

Mid PP (77-99) were only slight winners for me until I started raising with them from any position when first in, raising out of the blinds, raising from LP with limpers ahead of me and re-raising 2-3X bets ahead of me when on the C/O or button. Generally just being a lot more aggressive with them. Your pair is typically the best hand pre-flop and if you raise enough to isolate a single person you're still good on the flop 2/3 of the time against overs. Even if overs come, your strong pre-flop action allows you to represent hands that can induce better hands to fold.

My problem was that I was playing these hands too much for set value alone. They're strong enough though to play them much more aggressively than I was. I was calling too many 3-6x BB bets looking to set and snap of AA or KK. Well most 3-6xBB raises aren't AA or KK. I was calling off too many bets when I didn't hit my set and wasn't getting paid often enough when I did to make my passive play profitable. I now tend to treat mid-PP like they're the best hand PF, and most of the time they are. Even if they aren't, an aggressive approach allows you to at least make it more convincing that they are.
This is closer to the truth. Surely higher buy in games are far more aggressive and tight (or full of better players who dont make so many mistakes) therefore opening with a wider range not only makes us difficult to read but also will get action on out better hands.
Thus, if we only ever 3 bet or lead with good hands we become easy to read.
ABC poker has so many exploitable lines and is so easy to read too eg set hunters/overpairs etc.