Good luck dealing with the legal ramifications of charging someone to use your gear in someone elses venue to record an independent contractors music which has some intellectual property rights attached to it. I doubt what you had to pay to cover yourself could offset the small amount you'd recover in fees, even if someone was willing to pay for tapping in. In the end, I think the 'bad precendent' issue, while definitely valid, becomes sorta moot. IMHO, this is one of the reasons most bands say 'no' to SBD recording...it's not because the SBD is better sounding (which is a myth anyway), it's because then the FOH engineer and venue's might want a piece of the action since their time and gear are being used.
The 'freely traded, never sold' aspect of the taping hobby tends to self-correct alot of those issues.