b,
I've cooked so many spare ribs I sometimes think I am one. Too often they were hit or miss, tenderness-wise. Since I committed to BBs I haven't looked back. I'm happy, my kids are happy, but best of all the wife's happy.
I know everyone has their own favorite, spares or BBs, but as one who has had plenty of both I'll take BBs every time now, especially off the WSM. Just for what it's worth.
By the way, if you watch your local grocery stores you can get BBs for much less than $5/lb. I catch mine at the local store when they are on sale for $2.99/lb, stock up, and freeze them. I never pay more than that. Good luck on your ribs.