You definately need to buy more than 4 rolls worth to get results... unless you are just plain lucky. Usually if you get a box of dimes (50 rolls) you can expect to get 1, maybe 2 silver dimes out of it.
Hmm... just find two banks right next to each other and go back and forth $20 at a time haha
I used to be the same way as far as having free cash around to use. So I just ended up getting something like $20 in nickels at a time and after a while you can get some good finds from them.