Tom,
We were there for the first time in April with a corporate group. It was one of the BEST "corporate" trips we have been on. They had arranged tours everyday.
We loved Montserrat. I highly recommend going there for a couple of hours on a nice day. The views are stunning and the village and abbey are right out of a movie set. There is a mass at 11:00 that is open to the public so if you have a chance, step in for awhile to admire the beauty of the abbey and hear the monks singing on the altar.
Also, at 1:00, the boys choir sings for 10 minutes. Try to get there for that.
We also took a Gaudi tour - absolutely awesome. We missed some of the art tours but heard very good things about them from other people. There were so many things to see!
Have fun!