rak: yes. What I tried to suggest, is that your mix-it-up be focused: if your absolute limit is 80, sometimes bid 80, sometimes 70. They won't know which. They'll have to guess what to do. Players who think ahead, may well bid 80 over your 70, and get too high. More options open up when you have a higher ceiling...either you have somewhat more meld, or partner gave 30. The examples I gave, are somewhat constrained because the auction can never die below 65...not when it's double bidder out. If your preferred level is 85, but 90 is OK, then you can mix it up by starting with the jump to 70 occasionally. If the opponent jumps to 80, you're comfortable bidding 85. If he bids 75, you bid 80, and he has to think whether you're stretching.
mick: a common mistake among players who don't think about the whole hand, is creeping. FAR too many players in Advanced do this. Creeping is *really* bad when your limit is also fairly low, like 60. Say the auction starts 50-pass-pass to you. Your hand:




















25 meld and 7 tricks, so about 42. No extra chances, which is a negative. 60 would be aggressive, and hoping partner has a little something extra than the 15 you expect. You'll go down from time to time if you bid it. BUT, jumping to 60 will at times induce LHO to bid 65, and he may be WAY too high, or his partner may have a disappointing hand. If you creep by bidding 51 ("oh I want it cheap") he may just try to steal at 60...say he's got roughly the same hand, but with 2-4 more meld or 1 more trick. He expects to make most of the time...and he's forcing you to 65. The rule that you're forced up 5, rather than 1, is key here.
Creeping is clearly wrong when you have the information advantage...partner passes, RHO bids 50. Anything less than 58 leaves too much room, and I've grown to dislike 58. Bid 60.
To your point that you may not want to blast to your upper limit every time: true, you don't. But, that doesn't mean creep. Say you've got a nice 9 card, double ace run and a couple side aces, plus a double pinochle. That's 45; 9 tricks puts you at 67. 75 is VERY safe; partner will have to have a total dog of a hand. 80 is your comfortable level; 85 is your maximum. After 50-pass-pass to you...65 is fine. You may well buy it; if so, cool. You know you'll make, even if partner has absolutely nothing. If LHO bids 70...is 75 comfortable for you or not? He can't be sure. You could also start with 70 on the same argument, but that doesn't sound like a steal/bluff; it's too high.