NEX-7 or wait? HELP

1. Hard to say if the 7 is better built than the 6. Poly-carbonate is pretty robust but the 7 is the flagship model so it would be a good assumption. As to why the difference in materials? Cost, product differentiation, just to annoy us... who knows?

2. That's a huge can of worms. There are many arguments about this on this and other forums. Some people believe the 6 is better for low light situations and the some people believe the 7 will show more detail, others disagree and everybody has samples and science to back up their claims. The simplest answer is that for most people, there won't be a discernible difference in picture quality for practical purposes. Ease of handling could make a difference in what you are able to capture depending on your shooting style. I'd give this advantage to the 7, but PDAF in the 6 may give it an advantage in AF speed.

3. There is a new rumour about a 7m. If Sony is targeting a late 2013 release of a full-frame NEX, one could expect an earlier release of the 7's successor. While you might not be that interested in the new more expensive 7m, the 7 should be cheaper at that time, maybe the same price as a 6, and there will be many used ones for sale at that time too.

4. It's the same lens but in black. The 7 does not come with the new 16-50 pancake zoom. You might want to pick up the 7 body only or a different lens package.

I used to have the 5n and now have the 7. I liked the 5n very much. I absolutely love my 7.

Good luck.