Yes, Yes. But even then, I bet you'd still come out ahead by changing over the phone. Most mint legs I've seen are in the $599 range at most times of booking (BOS-SFO, BOS-LAX), with a +/-$100. Depending on what you paid for a regular Blue fare the difference will probably be in the $200-$300 range versus the $499-$599 gate upgrade fee.

Now, the BOS-LAS flights I've seen have had $1049 (!) mint fares, and in that case, you'd come out ahead with a gate upgrade.