With regards to the camera... it's a personal choice. I used to have an Acer A500, which had both front and rear facing cameras... never really used either (other than for a little bit of Skype - and then it was only the front facing one).
Manufacturer refurbs are as good as new - they wouldn't sell it if it wasn't working (they are often returns that they have repaired with brand new parts), so I wouldn't be too bothered. I do understand that you may want a brand new, un-owned device though
On price - you've gotta do what's best for you/your budget... if you can afford the extra, then why not go for it?
On space... as I said, it depends on what you're going to do with your device. Both my Nexus 4 and my Nexus 7 are 16GB... would have liked to get a 32GB N7, but the one I found on eBay was a steal, so I'm not too worried. I don't store loads on my devices and use the cloud more... again, this comes down to personal choice
One plus point, for me at least, about the Nexus 7 is that it's a Nexus device. I rooted both my phone and my tablet as soon as I got them and it was pretty straight forward (a lot easier than rooting my old Desire HD/my wifes Galaxy S). While I realise rooting's not for everyone, being a Nexus device means that there is a lot of love shown by ROM developers
