yes.
the weird rock formation is interesting natural spectacle. great views. fun cable car ride.
monastry itself no great interest.
tourist trap -pricey crappy crowded cafes.
take hourly train from Barcelona to Montserrat Aeri station whence a cable car whisks you to the monastery at top of rock.
no need to linger too long on top - its the going up and down thats fun -and walking around the local woods.
Taking the regular train means you can stay as long or as little as you like. In the afternoon the train is only every couple of hours.
You should visit Girona/Gerona I never understand why everyone seems to miss this - one of the most interesting old towns.
If you has a car drive along costa Brava -wonderful scenery.winding and dodgy in parts.