I have received several of these emails over the past few weeks. One I had a B fare but still in Y and they were telling me to buy up for like $140. Luckily I checked back often and snagged one of the last instant upgrades. The other was my trip to Vegas this weekend on ORD-IAH-LAS RT that they wanted me to buy up $175 on a ticket that was already $725. On those 4 segments I received 3 EUA's.