Google didn't really want to buy spectrum. Schmidt even publicly stated they had no intention to buy the spectrum. They were just after open access to the "C-block" of the spectrum which they got as a stipulation to them making a slightly higher than minimum bid. They got what they wanted, and it wasn't to own the spectrum.

With that said, I don't think google has any real interest in being a carrier, as that isn't where they make their money. They can leverage the mobile network much like the internet and continue to make their truck load of money via targeted ads.

I'm not so sure. The net profit margin of US carriers is half of google's. If they bought or launched their own carrier they would have to reinvent telephony as we know it or their stock and hence stock options would get slammed relentlessly.

The world is a lot larger than the US, by buying a local European carrier they would be able to do it without having to buy a major US party (which I guess would be even outside their pocketbook).