Yes, try the Dublin option sometime when heading over the Pond. The pre-clearance of US immigration means you arrive in the USA as a domestic passenger, and will therefore have more time to make a connection. Although several US airlines fly from Dublin, I'd avoid all of them; Aer Lingus is OK, but will only take you to Boston, Chicago or JFK. From Manchester, I'd take the Virgin direct service.
I hope you enjoy your trip to Las Vegas. I went there once and was quite amazed and astounded by it. People talk about culture shock when travelling in India or China; but Las Vegas was so far removed from reality - even by US standards - that it was like being on another planet. I'm glad I went, but don't think I'll need to repeat the experience. You can eat really cheaply (and plentifully) in the casino restaurants.