Starfox
Hero
You may want to consider replacing the roll for Aid Another with the pre-errata Easy skill DC from page 42. This makes it a roll of a 10 at low level, but it scales up from there.
When the party is 20th level and has a +10 for level alone, it seems like making them roll a 10 to assist is pretty pointless. If you want the roll to represent any effort at all, it needs to be a sliding scale.
Carl
My idea here is to add +5 at Paragon and +10 at Epic levels, thus making the DC to assist 10 (Heroic), 15 (Paragon) and 20 (Epic).
Also, if several characters at attempting a task together, I allow the players to pick the main character for the task after they roll. This gives a real, tangible benefit for a party to have several characters with the same skill. It also shifts the role-playing initiative around, especially on social skills.