It is the everyday things that you do that get affected. Fights are rare, at least compared to buying drinks from vending machines. Fights also last a short time, so the effect of the imagine breaker should be significantly lessened. Luck is all about probability. What I am proposing is that the imagine breaker is constantly removing luck, meaning the probability of him having trouble with tasks that he does all the time is much higher than something done once a month. This also applies to things that occur over long periods of time, simply because they are exposed to the luck removing power for a longer time, and gains a bigger chance of turning out bad. I just phrased it in a rather strange way to match the idea of magic and energy removing luck (which I think is bogus anyway).

About his luck... You have to consider that having all these problems in the first place is quite a streak of bad luck. Good luck is usually defined as when things go your way or even better than expected. He seems to be faced with one trial after another, which he only barely survives. He seems lucky if you view events in his life in the context of what is happening (like how he managed to defeat accelerator when he should have been pulverized), but such a life seen in the bigger picture is hardly lucky.

To put it simply, not losing the arm in the first place is lucky. Getting it reattached is mere consolation.

Of course, Touma is satisfied with his current life (as his father noted), and happiness is not defined by luck or how well things go for a person anyway.