Is this worthwhile? Yes. Well I would say that, of course, because I participate, but it's something that you won't really see anywhere else. Well, apart from the places where small groups have formed as the traditions fame has spread over the last decade or so. Like, for example, to the Castellers of Sydney who I think are still active.
How long should I allocate for the event and how early should I be there? I would aim for being there about 30 minutes early if you want to watch some of the preparations and also if you might like a drink at one of the bars with a seat - though you might also prefer to get up and get closer, especially if you're a photographer. I would think they will finish in between 90 minutes and two hours, maybe less. If they have a good day and enjoy themselves there might be an impromptu dance at the end, which is quite nice to see.
Would it be extremely crowded? I don't think so. The teams taking part are not the superstar teams that can build 9 and 10 level towers, however the location is a brilliant one which is already popular with tourists so there will probably be people passing through who don't even know it's happening but who will pause to watch.
How long does one team take? That's a tricky one. Each structure should take between 3 and 5 minutes to build and take down. However a lot of the technical skill involves getting the base and the 2nd level right and this takes time. Getting close to the action will mean that you can see the subtle and sometimes not so subtle adjustments being made.
Do they perform at the same time or one after another? With three groups together they will almost certainly perform individually. Sometimes when more groups are together, some of the rounds will be done with them building at the same time. At the end, they will almost certainly build pilars, and all the teams will build these together - it often looks quite impressive because each team might build several.
If it's sunny, take a hat and sunglasses, plus sunscreen and something to drink and wear your most comfortable shoes, which is good advice for any visit to Barcelona.
