Have you recorded how all of your opinions have gone? If you think something should be 1.15 when it is 1.20 why wouldn't you bet? I understand that alot of people like a larger margin (a bit of a buffer) but the thing is if you are more accurate than the bookies the bets will be profitable over time. You are right that it doesn't give much (any) room for error, so unless these bets have shown to be profitable you should leave them alone (which is why you should record them even if you don't bet them).

I'd just flat bet. You don't really know how much of an adge you really have on either bet so you'd want to be conservative.

If you don't bet the 2.10 you should still record it. If I was you I'd try to develop a system based on what your normal thoughts are, where you look for advantages etc. Test it over a few years of results.