I have noticed Dublin Airport security getting busier recently with a lot of holiday traffic so perhaps you do need the additional time. Not only has the volume increased but the passenger profile has changed. Generally, people who travel regularly (which form a larger proportion in winter) take less time to get through the basics because they know the drill, holiday makers can sometimes be ... frustrating ... if you are a regular traveller
For the American flights, I would check online at the
Dublin Airport website to see how many flights to the US are departing within an hour of your flight, I can see from the website that there certainly appears to be a few so I would bank on queuing for Customs and Borders for quite a while (New York 9.35, San Fran 9.50, New York 10.30, Chicago 10.35, Newark 10.55, Philidelphia 11.15, Boston 11.30).
Assuming a 9.30 - 11.30 departure window I would also check just how many flights are going out in general at that time, also I would look at the flight profile, are there several intercontinental flights? That means more persons per flight and hence a bigger queue at security.
I think it is safe to say you may not turn out to need to be there three hours beforehand but I don't think that two hours would be sensible either. It's a pain but I'd stick with the recommended time.
Oh and the DAA are not giving out the free bags for liquids, gels, pastes anymore. It now costs a euro for two bags in an annoying ball. Be sure to bring your own!