A few years ago I blew a tire.. Went to Wal*Mart and ask "How much for a new tire" As we walked back to the car the write up kid kept trying to tell me about why they no longer plug tires, just patch.. I told him I knew about that but how much for a new tire.. Finally I showed him WHY I wanted a new tire and he says "You need a new tire" Kind of surprised.. I ask him what I'd been telling him all along.
The problem is this, though a plug is a good short term repair it damages the bands in the tire and the chance of a more serious blow out go way up. I would not plug a tire unless I had no other option and then I'd get it repladced ASAP.