Can you go to t top and have a beer without paying to go through the museum?
No, the bar that is at the top is only for people who have gone through the building/tour and paid. You get your "free" guinness at the top. The bar is not that big and can barely hold all the people doing the museum, therefore outside people would send it over the top. The museum is worth doing IMHO. Guinness is such a part of the Irish culture. We took two hours to go through it. Buy your tickets in advance online to save time waiting to purchase a ticket. The view from the top, called The Gravity Bar is great!
No, but if you are a Guinness fanatic, the museum is worth doing. It teaches you a lot about how beer is made, and how to pour the perfect Guinness.
If you are not a beer enthusiast, your needs can probably be served just as well at any bar in Dublin.