I got my glider license before I got my private airplane. GREAT DECISION. I made up almost 1/2 the cost of the glider license because I got my airplane single engine land (ASEL) at 48 hours instead of the average of 60-70. My ASEL checkride was incredibly easy (because I had covered most of it during my glider checkride). My oral was under 30 minutes!! Oh, and whenever the instructor/examiner pulled the engine on me, it was not a big deal.
I think glider flying makes you a better pilot. I have outclimed a 172 in a 152 just because I slowed down in lift and sped up through sink. You develop real good judgement (because if you don't judge your trip back to the airport, you will have to land off field in a glider). And it makes your ASEL rating so easy.
You could probably get your private glider for about $3000 (aerotow), or even less if you train for winch-launching (kind of like an aircraft carrier takeoff!). 1/2 that cost will be made up when you get your airplane license. The other half is just worth it. Plus you get a lot of respect amongst pilots. I know many powered pilots who think I am crazy because I fly planes without engines.
It is totally worth it. I would recommend it.