The glass for me was a plus, it looks nicer, and it is gorilla glass i believe, which is more scratch resistant. As for shattering, dropping anything too much/too hard will break something. As for expense, Pre prices have dropped pretty low AFAIKAFAIKAFAIK. $Saw$ $a$ $couple$ $2$'$s$ $on$ $craigslist$ $in$ $my$ $region$ $for$ $$20$-$30$.
There are two variants as Remy X said. The CDMA is Verizon only, so no Sprint (without hacking and an already-activated Sprint Pre)
And the Unlocked GSM model can be used on any GSM network that allows it. So AT&T? Sure. T-Mobile? Check. Vodafone? Uh-huh. and so on. But CDMA networks (e.g. VZW, Sprint) are more common in the US and won't work.
The Pre2 is generally built better and expect webOS 2.x, which comes with it. (Unless you hacked your Pre+ to run webOS 2)
It's generally the same in terms of hardware, but a bit more tightened up here and there. Speedier with a faster processor and a bit better camera. (Still not the best by a long shot)
The screen is flat instead of rounded which isn't much of a problem unless you use one of those slide cases, which might be bit of a squeeze since the 2 is less rounded around the screen.