Ok, let's say you add your own IP in the exclusion tool and then a few minutes later, search for your main keyword. As you aren't visible I assume it doesn't count towards an impression so it doesn't effect your CTR. However, as you haven't clicked any of your competitor's listing, their CTR will go down slightly. This might result in their listing going down and yours consequently moving up. A true thought or do you think Google have that one sussed?
Might be true, but what if your competitors do the same ? Anyway if they DON'T and you do not refresh that search page thousands of time (Google might "suss" that) I think you're right - your competitors' add score will decrease.
Waste of time, as robertpriolo said its only 1 impression, this actually could work if you did it on a large scale and had a lot of different IP addresses (from different regions) doing this. I am sure if you use proxies that Google is aware of this so it would have to be done with real IP addresses (such as unblocked residential connections) also I think if you blocked all the IP addresses from showing your ads Google would know something is up so it wouldn't work so you'd actually have to let both you and your competitor's ads show then have clicks made on your own ad (which you could offset by then having them click on an adsense ad on your site), I don't think this is worth it or recommend doing it as its essentially fraud and could not only get you banned from Google but if you did this on a large scale they might take legal action against you.