Two problems with your thinking:
- You probably are thinking of doing GUF via a TA. Unfortunetly, as soon as you have another carrier in the ticket, GUFs cannot be applied anyway. Some may have gotten lucky but the rules say no dice.
- The TA instructions for GUF are designed so that you are supposed to get TPs and Avios for what you paid, not what you fly.
So no, you should not be able to get more TPs by using a GUF. I tried to use a TA to apply a GUF without success because of rule 1.