Subscribers would get more stuff, and that "stuff" would mostly be more carefully curated and organized collections of tools and plans. Possibly an additional new subforum too; not sure yet. For example, a collection of links to free sets of plans for homemade tubing benders. Or stuff like these:
I'd also like to take a portion of subscriber revenue and use it as prizes for more higher-dollar long-term tool building contests, that subscribers could enter. Instructables does a good job of this; of course instead of crafts and such, our contests would be all different kinds of tool contests.
Broadly, even if people wanted to (I don't) - privatizing entire forums to require paid subscriptions doesn't really work as a content model, because then search engines and other traffic source websites can't see the forum pages, and won't list any of them.