Does a greater devotion lead to more evangelism? Do it lead to feeding the poor preaching the Word? There is a old saying of one being so heavenly minded that they are no earthly good. So many want to eat at the Lords table but no one want to work in the field.
;-)
I guess the short answer would be that if it doesn't inspire it in the stigmatist, it inspires it in those who hear or read of him or her.
But to sort of spread it out a little, I'd say that the world "profits" from the prayers of the hole, and even from the prayers of such a moiself. While I think few are called to be hermits or 'enclosed', still not only histories of their lives, but their lives themselves benefit all of us.
Catherine of Siena, a lay Dominican and one of the heroes of our order, was a stigmatist and she was very active in the world, not only consoling and evangelizing, but writing and counselling. The cause and effect relationship might not be very clear, but nobody could say she hung around the house doing nothing. She seems to have been nourished and energized by her prayer.