@OP: the location and the people would be my top two concerns followed closely by date and time. all pretty practical obviously, but those would be the factors i'd base my decision on attending or not.
more specifically: must be somewhat close by; must have at least some nice people involved; must be on a date and at a time i'm willing to go (i'd probably lean towards a sunday early afternoon sort of thing, but i may be willing to attend in the evening during the week as well depending).

I'm sorry Prawn...you were right...