I have never used PP restaurants because I normally go to sky club or escape lounge at MSP. It seems the abuse is due to greedy people AND restaurants not checking boarding passes. If someone is legitimately flying out every week, s/he should be able to use the benefit every week.
The sure way to prevent abuses/fraud would be to change the benefits to reimbursement. You pay it upfront with your qualifying card and get reimbursed after submitting your boarding pass and receipts.