I know what I wouldnt recommend, and that's any type of spray. Detailers commonly use sprays to cover worn steering wheels and seats. However, as soon as the sun hits it, it will start drying out and will feel like paint.
I'm thinking about a re-dye instead. I might try out leatherique. Some BMW owners have used it with promising results. It's at
http://www.leatherique.com.
They specialize in rejuvenation kits for seats and panels. They also sell a $20 kit for the steering wheel that I think I'll try. If that works out okay, I might try it on my sport seat bolsters.
I'll post some pics.