I worked hard at building my stash in the beginning by buying yards of fabric "because I liked it" - then the left-overs from projects got added and before I knew it my stash was nuts. Some things are great to buy for stash, such as solids (particularly white, cream, black, and red) as those are my go-to colors for certain quilts. Other neutrals are good to have on hand too, but the specialty patterns......I have gotten really careful with what I add. I get neutrals on sale and the others are specifically for projects - no more "just because I like it" purchases (for the most part).
My space runneth over so I joined the fabric moratorium thread on the QB. Whatever you decide - make sure it gives you pleasure.