It seems counter-intuitive to me to re-use a single batch of Xtol until it runs out of oomph.
If you stopped after a few films,depending on your developer volume,you will have a "seasoned"batch of developer,which you can keep at a stable level of activity by replenishment.
Xtol,being its own replenisher,makes it more amenable to this than D76.
I first learnt about this on this forum - I'll never go back.
Thanks folks