From what I have read, breast stimulation never hurts, especially if you can manage it through a subsequent pregnancy when tissue growth is likely.
I supplemented from 6w-11.5mo almost exclusively at the breast with my daughter. She still nurses a few times a day at 2.5y and I am halfway through my second pregnancy. Obvuiously other factors could cause them, but over the last two weeks, I have seen an eruption of new stretch marks on my breasts, which I am hopeful means more tissue and a larger supply with this kiddo.
I anticipate nursing my first for 32-33mo total, then taking a break for 2-3 months before the second is born.
Mama to Raina (9/06) and Peter (8/09)!