Did they send you the offer in the mail, or did they call? If it was via mail, then it is just a sales tactic. If they called, then it would be more likely that they really do have a buyer in line.
I've gotten these offers in the mail in regards to my previous Nissan and this Lexus.
If you're interested in getting the new lease and they really are motivated to get your current vehicle, see if they'd give you the $450/mo with $0 down.