I've not been to the fair myself but I would hate to see it go as I think its a big attraction for the kids and there is little enough for them. The small percentage of 'undesirables' should not be allowed to become the cause for the facility being taken off the majority of decent people enjoying it. Let the Police take care of the trouble-makers.
I agree that the common should be in more frequent use than this one, annual event. However, Caerleon is a dormitory for people that work far and wide and want access to the M4 two miles away. Its not a community, and there are few enough groups in the 'village' to be able to organise any enterprise to put the common to good communal use.