I was talking to a friend of mine a few months back and we were thinking the same exact thing.
He's a Dolphins Fan, so we were talking QB's and of course Tua came up. (Which they actually did draft.)
He said, "Why go in debt with 1 QB when you can go get 3-4 run/option types for pennies on the dollar. You don't go in salary cap hell over 1 player. Plus, if that high priced QB goes down, so does your offense, thus the season is about over.
Now, with multiple QB's you have cap space, and if QB1 goes down, insert QB2 and keep the offense moving. It's definitely an interesting concept.