Gliding as a way to learn powered flight: tosh.
Gliding is an excellent way to burn money*, and an OK-ish way to improve some aspects of your flying skills once you can already deal with basics. Just like taildraggers (for the second point anyway, they're not especially expensive).
Advantages of powered aircraft:
1. They're what you what want to end up doing (presumably).
2. You can do this neat trick called a "go around" when your landing is terminally messed up - which is guaranteed to be often in the early stages.
3. You can fly for as long as you're likely to want to, while you do things like airwork.
4. You can go to other places - that you have chosen before you start the flight.
I could go on.
n5296s
* - my one brief experience of gliding was that per hour it cost me as much as the Pitts, i.e. a LOT. Actual glider time is inexpensive, but all those tows cost a fortune. Glider pilots talk about this mysterious thing called "lift", but we (me + instructor) never found any. And if you do find some, you'd better have seriously good flying skills to take advantage of it, since it involves flying steep turns on the hairy edge of a stall. Easy when you know how, potentially fatal before that.