Interesting idea... Thanks for sharing it...!
My first question would be - what do you get out of it? Would you make more money from it somehow? Is it a way to try to make the advertising sales easier? From what I can tell, you don't make more profit per advertiser (at least if you do, I don't see it specified...)
My primary worry would be this part...
"Generally, this would be done on the honor system, so make sure you trust the restaurant."
That means there is extra work for the restaurant... They have to track the coupons, and set up a payment system to pay all the people who make referrals, and do it on a regular basis.
Now, some might do this. However, based on the restaurant owner I know quite well, many restaurants are already flat out
and extremely busy. They often work from early in the morning, till late at night.
I once knew a guy who ran a food court restaurant inside a shopping mall. He complained to me that he never got to see the sun (especially in the winter), since he started before sunrise, and ended after dark, 7 days a week - and all those hours, he was stuck in the shopping mall! (He no longer runs that place... I don't know what he's doing now, as I've lost touch...)
Anyway, this requires the restaurant to do more work. That could be a "red flag" in the eyes of many restaurant managers and owners, who are probably already working long, tiring hours... I'm guessing that they don't really want more work to do.
In the way Don Alm structures his deals, there is virtually zero
extra work for the restaurant. They just get the benefits! I think that's quite important if you want the restaurants on board with the idea...
However, it's great to try to think up improvements. Everything can be improved.
Of course, the best idea is to go out and try it. You never really know until you test, and all my comments could be wrong.