I think suited portions of these cards only add 4% in your favor. So, what is your reasoning to prefer 76s or 98s against KQo?
You're right, you probably wont hit your flush with a suited connector, that's why you don't invest much to play them.
Your goal is to see a lot of flops with suited connectors and usually you wont flop a monster, from that point you either find an opportunity to take a small pot down or fold.
When you do hit your hand, you can win an enormous pot.
The other thing to consider is that having suited cards does only add a couple of percent chance of having the winning hand, but you're going to flop four to a flush a lot more often than you're going to actually make a flush. The semi-bluff value of this is worth a lot.
KQ is a great hand, it's really only dominated by AK and AQ (AA, KK and QQ tend to stand out and it's rare you'll stack off against them with KQ) but against a decent TAG you're not getting action from much that you have beat. Even KJ is probably only good to pay you off with a bet or two.
What kind of flop are you hoping for with KQ? Obviously anything with a K or Q and no ace will be most common, this is good for a small pot but against anyone but a complete idiot you'll usually only get a small pot. If you hit your straight you'll get paid (but there are only AKQJT and KQJT9 possible straights so it wont happen often). Two pair may also get paid, but could find it hard to get action since KQx boards tend to be scary enough to get rid of a lot of hands, and if x is A, J, T or 9 you could be dominated.
A hand like 78s though will often get action when it hits two pair or any of it's straight possibilities. It's flush being only 8 high can be troublesome but if you're aware that you only have an 8 high flush and keep a lookout for bigger flushes you wont get into trouble often (don't be an idiot by playing it like you have the nuts just because you have a flush).
Basically, when you hit for more than a pair, 78s will be a better hand. Against weak opponents maybe top pair is enough to win someone's stack, but against anyone with the slightest idea of what they're doing you usually need more than top pair good kicker.