Commercial nuclear fuel would be a poor source of plutonium. The production reactors we used to run in this country for the weapons program (we don’t anymore) used high density, highly enriched fuel that attained very high burnup. Those were optimized for plutonium production, Commercial power plant fuel isn’t. You can get plutonium from it, but it is a lot more work. Plus you’d have to set up a plutonium processing plant. Not an easy thing to do. An experienced national program can do it. An inexperienced national program can do it after a time (like India did back in the 1960s). It’s unlikely that groups below the national level can do it (on their own).
Enough weapons grade Uranium to make a bomb can be easily carried in a backpack, or handled with bare hands, without any adverse short-run health effects. It might increase the risk of cancer, but exposure will in no way impede a person from doing something with it now. Plutonium, on the other hand, is so toxic that it can't be easily smuggled or handled without very expensive, specialized and rare equipment. A terrorist attempting to do either would get very sick and possibly die before he would either get to his destination or make a bomb.
Hence it is very unlikley terrorists could steal plutonium and smuggle it to their camps, much less use it to make a bomb.
Weapons grade Uranium, on the other hand, once obtained, would be very easy use to make a primitive bomb.
Rougue states like North Korea & Pakistan are another matter, but they seem to be having little difficulty getting their hands on weapons grade uranium, so I hardly see how an increase in the availability of Plutonium matters.