Hand 1:

Remember that the purpose of a bet if not just for value is to fold out hands with equity against yours, not just hands that are actually ahead. With two cards to come you probably have less than 50% equity in the hand even if no one else has a pair (you can play around with possible hands for them in pokerstove). That said I seldom cbet 4 way and even on this board I'm not sure you get enough folds to make it better than checking, particularly when you have a fair amount of showdown value. If you're comfortable with compounding probabilities then it's pretty easy to work out whether the bet is good here though, since nobody's going to be calling you without a pair. (Just ask/pm me if you need help doing this.)

Hand 2:

I would question whether even such a nit as this folds any pocket pairs preflop in this spot. But yeah, irrespective of this it does seem like an obvious spot to check down, certainly if he's seldom going to bluff you off the best hand.

Hand 3: I think the more important factor here is that the board hasn't hit you very much, so many opponents (both decent and bad) are likely to try and make some kind of a play here sometimes. If I choose to cbet in this spot (which I would pretty often) then I will generally bet quite small (half pot or so) and be prepared to fire two barrels a lot of the time. Unless you know your opponent is very passive I wouldn't expect him to let you showdown K high and win very often without calling at least one bet (which I'm guessing you don't want to do).

Hand 4: I don't like a cbet here at all. The big differences between this hand and hand 3 are:
1. You have showdown value against his C range hands. So when he decides to check down hands that he thinks have showdown value, such as A high and weak pairs you will sometimes win.
2. You have virtually no equity against his stronger range, since you only have 2 outs to improve instead of 6 in the case of the KQ hand.

Hand 5: Yeah I check this also.

Rather than thinking just about whether your opponent is calling with worse or folding out better, you need to also think about how much equity you are folding out. This equity can be in the form of opponents with better hands, live outs and also hands that will bluff successfully if checked to, but will fold if you bet. Remember that against many opponents your hand only has showdown value if it beats hands in his C-range (unless you're willing to call a bet) since his D-range will usually bet at some stage. (See the the 66 and KQ hands.)

Another way of thinking about this is whether a cbet makes your opponent's range more or less balanced. A cbet can easily be justified even with a hand that only gets called by better/folds out worse if your opponent never floats, but will bet a balanced range if checked to, such that you have no effective value against him. If your opponent does float a correct proportion of the time then you lose the value in this cbet since he can still have a balanced range on the turn (so you can try double barrelling or checking flop more).

I think I had more to say on this but am knackered now, so may write more another day