Rodrigo Istalindir said:
One the things I've noticed in 3.x is that the skill system pushes most characters into being one (or two) trick ponies. The combination of very limited skill points (except for rogues and now bards), cross-class costs, and the cap, meant that everyone just maxed their class skills.
In order to keep skill checks meaningful, DC's had to rise. No longer were you making a balance check to run down the ramp, now you were running across the proverbial ice-covered beam. The result was that at later levels, skill checks seemed to become either automatic success or 'don't even bother rolling.' Certain checks became trivial for PCs that had it as a class skill, and impossible for those that didn't.
Your problem is in the bold text. You want to keep skill checks "meaningful." And by that, I suppose you mean "difficult" or "risky." Resist that temptation and just let the character who maxed his balance skill run down the ramp while everyone else walks carefully or risks falling. If he's a 15th level character with max ranks in the skill, he's one of the best balancers in the world, why not let some checks be trivial for him.
Doing this will have several effects:
1. There is no more "don't bother trying" unless it's something an unskilled character really shouldn't try--like swimming across the English Channel wearing fullplate. A fighter with Endurance, a modified 28 strength, 22 con, 23 ranks of swim, and a luckstone can do it. Other characters can't... and shouldn't be able to. However, for things like swimming across the local Olympic pool, it's trivial for that fighter (as it should be--he could do it wearing two tower shields and fullplate), but are still possible for other characters.
2. There is less incentive to maximize skills for truly sick bonusses. If you always seem to be pushed into situations where your current ranks make the task risky, then any character is going to want to get better so as to meet the challenge he already faces. If, on the other hand, you run across a lot of fixed, (relatively) low DCs, then there's a reason to say, "OK, I'm good enough now, let's focus on something else." How many characters in 3.0 stopped putting skills into Tumble when they reached a +14 tumble modifier? Even if they could get a few more abilities by going higher (tumble through an enemy's square automatically without provoking an AoO), the ability to usually (absent circumstance penalties, etc) succeed on the most common tasks was enough for most players.
3. There is more incentive to have mediocre skills. If every skill check that comes up in your game is "meaningful"--ie. challenges a max-rank expert--then characters who were thinking about spending some skill points there can observe that there is no difference between a +2 bonus and a +7 bonus when the DC is 28. So, why bother? But, if the party regularly faces DC 15 and DC 20 skill checks, even if they're automatic for the guy with the +20 modifier, +7 is better than +2 so there's a reason for the non-experts to buy a few ranks.
I'd like to re-work things so that (A) cross-class skills become attractive places to spend points, and (B) those skills generally considered critical (eg Spot) don't end up even higher than they are now.
One option I've considered is to have the same cost for class and non-class skills, and lowering the max rank to something like (LVL/2+Stat Mod).
Whatever mechanical changes you make, it won't make any difference unless you change the incentives. It is the need for "meaningful" skill checks that removes the difference between +2 and +7. It is similarly the need for "meaningful" skill checks that keep critical skills as high as they are now. (If most bad guys could be spotted with a 20, you wouldn't see many characters with +30 spot). You need to add more relevant skill checks with DCs between 10 and 20 to the game. If spending five ranks on balance enables you to run down the slope, people might do it. If it's always an ice-covered tightrope, then there's no point in the five cross-class ranks: they won't help.