Remathilis: You could make a better example that doesn't debunk itself as quickly, but the basic problem would still be there. If you present a challenge that is beyond that of what ordinary people can do, its always going to be an individual challenge, not a group challenge unless every member of the group plays a similar character.
Remathilis said:
Often times, unless the PCs had no choice, if a task involved a skill they were untrained in (and a real penalty for failure) they'd skip it and send someone (if any) who had ranks in it because they KNEW they'd fail but the guy who had ranks would most likely succeed.
If there is a real penalty for failure, then smart players are going to avoid the obstacle unless the probability of success is nearly 100% and the loss incurred by failure is less than the reward of success.
In the example you site, I'm not sure that even my rogue is going to try the three disks unless I have a feat that lets me take 10 on my jump and balance checks regardless of the situation. I probably wouldn't attempt it with one disk, much less three. The odds of failure for are hypothetical rogue are 19% (roll 4 d20's no 1s) with the results of failure being falling into the lava and dying. I don't think so. I'm going to be looking for alternative solutions, because there are only so many chances of death you can risk before you die.
No one else in the party dares that jump. The fighter's odds of death are still nearly 100% even with the SAGA rules. So nothing changed. You still avoid anything that isn't what you do if there is a significant risk involved. The challenge is still about the one character that can do it.
Before you go trying to tweak the example, there is something even more important that you are missing that is going to haunt any example you come up with.
All you've really done is created power inflation. You can set those DC's to whatever you want. My generally strategy for a group challenge is to set them to whatever would be slightly challenging for an ordinary person or athelete. In other words, I'd select DC's more around DC 5 than DC 15. In some cases, I tend to throw out DC 0 challenges where the idea is, 'This should be fairly easy, but if you have some sort of penalty (dump stat, armor check, flaw) you actually have to pay for it in risk.' So, with a slight variant on the encounter you suggested - DC 5 for the jump and the balance check and a 30' spiked pit rather than lava - I can challenge the whole party _as the system exists now_. For the example you suggest, all that you've really done with the SAGA system is increased the size of the numbers.
In both cases, pursuit is going to come from those characters where atheletics is thier thing, and the other characters aren't going to shine (or shine as much) or they are going to use one of thier strengths to face the challenge in thier fashion (cleric summons a flying create to use as transport, wizard casts fly, fighter resorts to long range missile fire to take down imp, etc.) Or, rogue gets to jump across the rings two at a time (awsome!) and the rest scramble along behind as best as they can while reminding themself what the 'Use Rope' skill is for.
IN SAGA:...Even if the bonus isn't all that high, the fact it allows them to attempt them rather than setting the DC so low the rogue isn't challenged or so high that the fighter, cleric and wizard can't succeed.
Except, as I've shown, that's exactly what you've still got. You've run into a famous engineering law: "if the probability of something isn't 0, then its damn close to 1." In this case, if the character's probability of succeeding in each step isn't 95%, then the chance of failure is nearly 100%. In both scenarios, the rogue has a near 100% chance of success, and everyone else has a nearly 100% chance of failure. So you've added only power inflation, while rendering the more trivial ordinary challenges outside of these specially designed scenarios pointless. No net improvement, no easier to design for (as your failure with this example demonstrates), and loss of flexibility, flavor (most instances of a class have the same skills) and versimlitude ("What do you mean my desert nomad can't swim? Haven't you heard of oasis? Maybe he learned to swim cooling off in the cistern! By the rules I qualify for being just as good of a swimmer as that fighter over there who spent his youth as a polynesian fisherman!").