The EU investment argument sort of reminds me of when I cancelled my last phone contract to move over to Giffgaff's unlimited data sim. The guy trying to stop me from changing asked why I was moving. I said that I wanted unlimited data and I could get it quite cheap elsewhere. The guy said "But I'm looking at your data usage on here and you never hit your limit". I said something along the lines of "well obviously not, you guys charge an arm and a leg if I do!"
Yeah, a lot of our trade is with the EU - because we're in it. That doesn't mean if we were not then we'd simply lose all that trade with nothing to show for it. Being in the EU makes it easier to trade with EU countries and harder to trade with others. Almost all of the countries who are a) in Europe but b) not in the EU have much larger exports to BRIC countries as a proportion of their GDP than we do. If we're to align ourselves anywhere, looking forwards, I'm not sure you need to be "bonkers" to prefer aligning ones trade agreements with the BRIC nations rather than the sick and tried EU countries.
Incidentally, one need not have 27 sets of goal posts. If we left, we could still have agreements with the EU (just like many other countries do, and like the US is negotiating right now). We might not get one, of course. But the remaining 26 countries would still have a single set of goalposts. If they want to stay in their union, so be it.
Despite this post, my mind actually isn't made up on the issue of the EU. But I certainly don't think one has to be "bonkers" to be on any one side of the debate. It's no where near that clear cut.