Wait, you're debating an 8gb touch to replace an 8gb zune? Why would you even consider the same size that you already have?
I've got a 32gb 1st gen w/ a bit over 2gb of apps (126 apps). You'll go higher if you have decent games, and since 4.0 supports over 2.1k apps, I wouldn't worry about filling it up with random crap.
Might as well get a larger version. Ditch the Zune if you're getting an iPod Touch (there is no such thing as an itouch). If you're keeping the zune for music, just get a larger iPod to fit music + apps. It's ~$199 for an 8gb, and ~$299 for a 32gb model. If you can save up for an extra $100, it's a no brainer.
This being said, if you'd like to have a camera... Wait till the next gen gets announced.
New models should be announced shortly. If the camera isn't a big thing for you, wait till the new models get announced, then snag one of the 3rd gen models (the ones that are currently out) with some discount.