1) No. It affects all G15 panels whose owners have the issue and post in this thread that they have the issue.
2) Depends on how bad it gets and whether you can live with it. Part of this is dependent on your lighting environment. If you watch with the lights on you probably won't even notice it. Lights out is where it'd be more noticable.
Like I've recommended before, I'd stress-test the unit for the first 50 days or so with content like planet earth or something else that's full 16:9 running whenever you aren't around so you can see within the first couple months (which should also be within your credit card chargeback territory) to see if your set is affected.
Panasonic is aware of the issue in some sets and there's indication from what they've told people that they may be working on a fix. You should be aware that while those with the issue are understandably the most vocal, their number vs. the amount of people who bought the sets overall are fairly small. It's still a very real issue, should you get it, but it's not omnipresent.
There's a tendency with consumer electronics for people to assume that any issue with a product is indicative of the entire product line instead of the individual copy they received. I believe there's a real issue here and I said that back when other people were trying to argue that it was just people's imaginations, but a real issue existing is no reason to run away into mass hysteria mode.
If I get a pack of pencils and one in twelve has no lead in it, then I'd probably just toss it away. If it was an expensive pencil, I'd contact the company and have them send a replacement (or if it was an electronically controlled pencil that was refusing to write, I'd have them make a fix for it). Now if you figure the same issue was present on x percentage of that product and those people all get together online to talk about it, then it comes off sounding like every one of the pencils have that problem. That's my impression here.
It's a real problem, one that Panasonic needs to address and fix, but from what I've seen it's isolated in scope.