A couple thoughts:

1) I don't think you will find any airline that will upgrade you on a consistent basis for international flights without using miles or an SWU.

2) Given that you do buy full fare tickets, I actually think DL is a better program for you as a DM as you get 10 SWUs that should help reduce the amount you have to dig into the miles. The advantage for the other programs would only be if you were buying cheaper tickets.