I think it's also a matter of principle, though. The EU has shown itself, in the last few years, the lack either the political vision or the institutions to solve the problems they have. Every single country is seeking to reduce their budgets - and you have countries like Greece where this is actively being forced upon them by some Eurozone countries and the ECB - and yet the EU think that it'd be best to divert more of the funds towards them. That is to say, that every cut to a benefit or a government programme needs to be larger than it otherwise would because the EU wants more of its member states money. I think this shows not only a bizarre sense of entitlement from a group that's proven itself incapable, it also shows the horrible disconnect between the EU parliament and the people they're meant to represent. The further away from the people a democratic institution gets, the more likely this disconnect is to occur, IMO, and it's exactly what's happening.
Now the reality of the situation might be that, thanks to the free trade agreements, the EU member nations have become our largest markets - but has there ever been a time that they weren't? They are, afterall, right next to us. We have this year though, for the first time in a long time, got more exports going to outside of the EU than inside it. The EU still has a plurality, but not a majority. So I think the question goes beyond mere short-term political expediency, and becomes one about whether or not we even want to lend our name to an institution that's proven itself dysfunctional, and that routinely does things that the UK electorate don't want (or, rather, the British MEP's are rarely on the winning side of any legislation passed in the European parliament).
