FWIW, I belong to Vistage, a large international CEO group. They charge premium dollars to exhibit at their events but beyond the business cards you can get at the event, they won't supply you with the member information. Same with NAVUG/AXUG (the Dynamics NAV & Dynamix AX user group organizations)
As a vendor, it makes it worth less to me. As a member, it means I won't be getting called 20x per day so its a hard decision.
Maybe a fair compromise is a gentleman's promise (in the agreement) that says they can email or snail mail, but not directly run telemarketing campaigns. Also, we coiuld make their life a bit harder by not including any phone numbers.