I would buy at least one, as I buy one or two Vegas ones most years - one for us and we sometimes give some out as presents.

Personally I would prefer the 24 month version that we get when we buy Vegas calendars - that was you can give them as gifts during the year and they will have at least one full year following which makes them a good gift (with the 18 month version, if you wanted to give one as a gift in the early part of the year you may only have 8 or 9 months left). They would also still have 18 months left if you sell at the convention, but you could still sell some in advance and as long as people buy one I don't think it would matter much if not everyone buys them at the convention.

Personally I wouldn't want too many personal messages in the dates - I would like some space to be able to put my own reminders and dates etc that I use my calendar for, but they wouldn't stop me buying one!

Overall a great idea though - go for it!!

Jason