Many clients wouldn't find this sufficient for user acceptance testing.

Won't any mildly tech-saavy client want to try it on their laptop, phone and/or tablet to make sure it looks right in different browsers? Well, it'll look exactly the same, because they aren't actually rendering it....

The minify/obfuscate solution seems sufficient (and possibly an expiration date...) but even that would be obviously unnecessary with many clients.

It would be interesting if you could render a Flash depiction of a live website and allow interaction without degrading performance or having it "look like Flash."