I wouldn't get too excited at the prospect of the mythical pre-clearance facility at Dublin. I have tried it once, having believed all the hype. and I didn't really see much benefit TBH.
Once you have an ESTA and are not using it for the first time, immigration at the US's main airports is now becoming a doddle. Or if you're Global Entry registered it's an even bigger doddle.
The people who will benefit most are the one-off point to point tourists who are looking for the absolute bargain bucket fares - and for that try the non-stops from Thomas Cook from your local airport.
If you're a returning ESTA or Global Entry ie a regular (read higher yield) pax, you'd be mad to go through Dublin.