Dry brushing, getting an actual piece of leather or vinyl and pressing it into the surface while the paint is semi-dry...all decent.
There are many faux-suede aerosols on the market that are convincing and if the finish is too matte, it can be shined up gradually using a polishing compound and a q-tip.
Grain can also be simulated by stippling with an old brush, preferrably one that has not been well maintained and is a little stiff. I agree that using a wash just slightly darker than the seat color to get into the grain and make it stand out is a great idea.
Simulating brand new, modern leather (flat finish, usually pulled tight) is different from aged leather which has a definite shine and wear to it.
This is what I'm going to try on my 68 Vette, but it's a very advanced technique (be brave, Grasshopper):
http://www.briansmodelcars.com/tutorials/tutorial.asp?TutorialID=40&CurPage=1
Good luck and if possible, post a photo when you're done :o)