Gather round, friends, and I shall regale you with tales of this mythical system once more. Yea, and this day the tale I will tell is about how d20 Rethought addresses several problems which seemed inherent to the use of specialized roles among player characters.
How does a system do such a thing, you inquire? Well, ask those who went on create the fourth edition o' Dungeons and Dragons, and they'd have spun you a tale wherein all the classes possess equal amounts of ability in the realm of combat, whilst the use of other skills was kept to an abstract minimum. But since you've questioned me instead, the answer will come in three parts.
The first and most fundamental factor is that high levels of ability in a given area does not translate to a higher check bonus. Optimizing your bonus on relevant die rolls in d20 Rethought is a simple process, involving only a couple of feats; "step 1" on the road to becoming a master swordsman/thief/etc. After that comes the feats which grant you Tricks, those various sets of moves which expand your strategic options involving a given skill- at the price of Resolve or Vitality points, your fresh-every-encounter first line of defense against mental and physical attacks. To restate the usual metaphor, you draw power from your shields to fuel other ship systems.
In other words, a high level of ability in a given area means a wealth of gameplay options, and a low level of ability doesn't render you ineffective. Other players don't stand around and twiddle their thumbs while the specialist does his thing, and the specialist isn't getting cheated on play complexity just because he's chosen an area of expertise that isn't combat-related. The idea is to make the specialist the resident authority when the gameplay focus is in his direction, creating a "follow the leader" scenario rather than a "stay back and watch" one.
This ties in nicely with the next bit of info: Some tricks for each skill are oriented around letting unskilled characters join in without ruining the group's chances as a whole. This is a direct mechanical attempt to head off the situations in 3.5 where the group can't act as a whole because each additional member is just another skill check that could result in a failure and thus ruin the whole deal. Here, with the experienced member's guidance, everyone can participate.
To further improve the group participation, we have the third factor: a core rule change allowing Aid Another actions using different skills. If an ally is attempting to make a good impression, you can aid his Diplomacy check with your Knowledge of the local culture or a Bluff check to strategically embellish on his points.
Together, these three factors should hopefully even out most of the wrinkles produced by party specialists, while keeping the benefits- after all, it feels good to have someone on your team who's an expert at handling a given kind of challenge, and it feels especially good to *be* that person.
As always, thoughts and feedback are welcome.