Meh.

If you're using GA to prove your site's worth, e.g. in some M&A deal, this is useless - your proxying means that you can fudge numbers and thus is no better than anything else you say. (This is a significant use case among looking-for-exit startups).

If you're using GA to get insight about your website, it would be somewhat useful, but not really - because GA would not be able to correlate the cookies to figure out the demographics, etc (and I don't know how much it would trust Via / Proxy-for headers, so other statistics it gives you are also limited).

Also, if you have non trivial traction, you're going to get flagged by their fraud filters.

You're probably better off running a local Piwik or whatever it's called these days.