I'm wresting with your same thoughts. I thought the sound system would be a big deal to me. It isn't. The HK (AKA Samsung sound system) isn't all that much better than the 9 speaker system. Yes, more base due to the speakers under the
seat, but spend a few hundred at a stereo store and they can replace the 9 speakers or a few of them and make things sound terrific...
The GT does have the GT look on the front end and rear. Back-end not such a big deal to me, but take a look at the GT vs the Base/Premium and it is different and not as aggressive. The 19" rims provide less roll and I prefer that.
Maybe you a sunroof guy? I've never owned one and it's not a huge deal for me. I fact, not having it brings more headroom and space to the back
seat. W/sunroof, you lose about 2.5" of ceiling, so if you ever have tall backseat passengers... Just a thought. But I've never wanted to pay $2k or so for a sunroof.
And the base/premium does provide better gas mileage. 19/25 vs 22/29... Thus 21 vs 25 mpg. For my driving case, (24k miles a year), burn all the math down, it's roughly another $500 more in fuel costs for the GT, or another $41 a month more. That means a lot to me, but wow, that GT is just so fun to drive.
If you haven't yet driven the GT, might I suggest you NOT do it, if you want to save money long-term and in the purchase price and stick to the Premium. Boy, tough choice. I still might not know until the last few weeks before I pull the trigger...