My 2 cents ... I think you have to be very careful not to generalize that all Jems will turn you into Yngwie (or whatever axe you happened to play that day at GC). After you shred on the Jem at GC, drive down to the Mom & Pop music store and see if the Jem there plays the same. Sure there will be general characteristics attributed to a guitar that make it a better fit form one person to another, but sometimes very small differences in how a guitar is set up can make or break how it feels, even between two identical models.
My advice ... if you played a Jem at GC and it was an out of body experience ... then buy that guitar. Last year I played 4 different Deluxe Teles in the music store, and one of them just melted in my hands... it was absolutely unreal how that thing felt and played. I had a few hundred bucks less than the ticketed price in my pocket and made an offer ... but the guy turned me down and I walked out of the store without that guitar. To this day I still kick myself in the ass for not ponying up the extra cash and buying it. I have yet to play a Tele (or any guitar) that comes anywhere close to feeling like that one did.
Footnote ... worst feeling / playing guitar I ever owned was a Jem... and I even had my first wife walk down the aisle to Steve Vai's "Liberty" (true story), so that should tell you how much I really wanted that guitar to work out for me.