Yes, it will pay for itself! It's phenonemal. The only downside is a manager will have to sign off on it everytime. It's a bit time-consuming but well worth it, especially if a bottle of wine is ordered! Warning: you may have to call and bug them about getting your card out. They're very slow about response time, at least they were. I ordered mine originally on January 10, was not even billed for it until May! They kept having me download a letter of permission and having to refresh the dates until I actually received my card.
We tip on the total amount, not discounted. I find the waitstaff at the Disney restraurants (majority of them) well worth the extra few dollars.