Looks like you've made your decision and I hope you really like the new car. They are definitely "prettier" than the 1st gens. I also went from a 1st gen (a Frosty) to an '09 Abyss. The GT. For me, I wish I would have thought more about how I
used the 1st gen. In hindsight, I would have picked another 1st gen, but all I was thinking was "I love my old Vibe, this one's newer, and therefore I'll likely just like it even better." While had I thought about the way I actually utilized my 1st gen I would have recognized the many differences.
I packed my 1st gen with any number of things on a very regular basis. The cargo area of the 2nd gen is more than a little smaller. It might have only slightly less floor space on paper, but the roof is not as high and the hatch door is not as big, and both of those things have a big impact on what you can haul and how full you can stuff that cargo area. Car camping now requires using the backseat floor space AND the passenger seat and floor space. And I'm only one person! (the back seat is taken up by a large dog) A family would have a real time of getting everything packed in for a camping trip in the 2nd gens.
I used the window. Not as regularly, but I did use it. Not having it is another, smaller, annoyance.
The GT doesn't come with roof rails, and although I think the 2nd gens look better without them, they are a pricey add-on when you are already loosing space in the cargo area so the roof becomes the only alternative if you still need to use that car for hauling anything.
And there are the cosmetic issues too. Pontiac's signature red dashboard is gone in the 2nd gens. There's a splash of red, but it's an overall more generic look and just doesn't have that standout Pontiac styling of their traditional red dash. The radio is hideous. Nuff said on that. On the Bases, you aren't getting anything special in the cloth interior either where as at least on the GT there's a little flare there.
But bottom line, if you just really like the 2nd gens then I hope you really enjoy this new Vibe. But I would take a moment to think about how you used your 1st gen, and if you utilized the "utility" aspect of the Vibe in your 1st gen, the 2nd gen is going to fall far short. However, if mostly you just used the Vibe to do your daily commutes and after-work errands then the 2nd gen is probably going to be more fun.