Went on one on the vertigo tour in Brussels , because it included a gold circle ticket. Had a few sandwiches and a couple of drinks in a bar near the venue and afterwards we had the surreal experience of a U2 tribute band. It only cost about £30 extra than the ticket on it's own would have cost, so for me at the time it was good value.
This time around they don't seem as good value, so I won't be bothering , even though I need to find a way to get into the Paris gigs