I've been to both, and I would definitely recommend that you try VIR. Both are excellent tracks, but having only been to the Glen, you'll learn a lot by driving a new track. I'm a firm believer that the more tracks you drive, the better driver you become.
VIR has a wider variety of corners than the Glen, so you'll definitely be learning some new things. The Glen really doesn't have any slow sections, and you never see 2nd gear there. VIR has two slow sections. Oak tree is a 2nd gear corner, and the 4-5 section is either 2nd or 3rd depending on your speed.
VIR also has some really high speed sections such as the Climbing Esses, and South Bend which is a very fast left hander following the Esses. In my car the VIR Esses are much more challenging than the Glen's Esses. At the Glen I can easily go flat out from turn 1 through the Esses all the way to the Bus Stop. At VIR, I can do the Esses flat out, but everything has to be perfect - car setup, fresh tires, a perfect line, and a willingness to experience a very high pucker factor.
VIR is narrower than the Glen in most places, so there is a premium placed on driving a very precise line. Also, at the Glen you have positive camber to help you in most of the corners. You don't have that at VIR, so that will take some getting used to.
If you're going to make the trip there, make sure to sign up for an event where they're running the full course. Often times they'll just be running the North or South course, but that won't give you the full VIR experience.
