Re: Elder Races...
1. I give them a skill, usually 10-, that lets them just... know something occasionally, or maybe use a small one time race-based power.
2. Describe that their eyes seem to betray an ancient wisdom, animals seem to respect the Elder more, they don't get bitten by insects, they never have to clean themselves, anything that makes them seem more.
3. I usually don't allow PC's to play them, unless it's a... young.. Elder. It gives the player too much superiority over the other players. From what I've seen, it also creates too much reliance on the Elder's powers and heritage.
4. If handled carefully, they add. If tossed in as a solve-all, be-all, uber race that could do just about anything, they suck.
5. Mri, from the Faded Sun trilogy by C. J. Cherryh. They're powerful enough that in the books they're talked about in that no human would ever want to fight one on-on-one. But.. they're not overpowered. They have a huge honor system, which also adds to the mystery.