I went for the series two for a few reasons. I realize that this probably makes little sense to some people but for me, once you're up over $400 (CAD), what's another $129 to get the latest and greatest? I know it depends on the perceived value for that additional $129, but for me it's worth it for just the brighter screen and the waterproofing.
The brighter screen isn't likely to be a huge factor on a daily basis I admit, but when you're outside on those crazy sunny days it would be nice to have a little more "pop". As for the waterproofing, I'm not a big swimmer, nor do I do laps. That said, I hang around pools and cottages in the summertime and it's not difficult to imagine a scenario where I forget to take it off before swimming....or I'm pushed into the water by someone. I consider the extra money to be an insurance policy to protect me from accidents involving water and yeah, I'll probably wear it swimming if the option is available.
I'll also use the built-in GPS as I do try to run on a fairly regular basis. I'm not ready to drop more money on blutooth headphones quite yet, but having the ability to go for a run sans phone is another mark in the "plus column".