Not the only way at all, a few of those models were kept for a short while only ,bought cheaply as last year models and traded up for next to no outlay ,i got rid of the GT50 after a very short while ,moving up to the GT60 which was superior,this in turn was sold to purchase the ZT at nowhere near the list price ,this i kept for 1.5 years ,sold to buy firstly the 960 ,then the 950 old,which all told cost me less than 400 pounds !!
Is there a problem with changing sets every year though ? certainly in my eyes there isn't,if your good at judging the market it can be done with minimal outlay,technology moves so fast ,theres always something better !
I think you stated you would only part with your GT50 for a major upgrade,well let me tell you this ,going from a ZT65 ,to a 950 OLED is a major upgrade in every department,so coming from a GT50 it will be a massive upgrade !!