I've never foiled baby backs...seems I can get them "falling off the bone" (which I personally like) with about 5 hrs of cooking time.
Spares, I think, are another story. I never liked spares much before I tried the 3-2-1 method. I like the way that you can get the spares to the same consistency as a baby back...without the longer cooking times.
I guess all I can say is that foiling spares has worked really well for me. But I don't think I'd ever do it for BBs. Glad your cook turned out well!