I have personally had such pet OCD that I do have a ton of unused stones. I think that spending time doing better things than worrying about dragon upgrades is a fair thing to do. There aren't that many dragons compared to other families to use stones on. On top of that, there are is only like 1 pet that is worth stoning and selling. I think that by far, most of the dragon pets come from special circumstances and as such are rare to begin with. CE's, achieves, raiding with leaches, etc.
Plus, if you happen to get a beast or flying stone, there's a very good chance that you would be able to trade that for possibly two dragon stones for the vender pets, etc.
Just my 2 cents.
<Kings and Queens> Alliance on Dawnbringer
-pet collecting OCD