Generally what leads me to looking at changing clubs is if the new club looks appealing to me. I guess you could say it's a physical attraction at first and then the work begins.

I'll spend time on the range and of course a good proper fitting with the potential new gamers before I commit.

The longest time I've owned a set of irons was 10 years. I started golf late. They were a game improvement set and they had a graphite shaft- a Japanese brand that my dad helped me get with some fitting. It worked well for me. Then I played a friend's set with steel shaft that got me hooked because of smaller or tighter dispersion. From there, I went from brand to brand for a while before I played Titleist- I was afraid to play it. My step dad and all his friends play Titleist. They were all very good players. They were all in the golf business- either a golf equipment rep or pros at high end courses- a couple of them were Titleist reps. They were also all PGA- some retired from tour others just tried to breakthrough but still in the golf circle, they're just all good players.
One day when no one was looking, I remembered fitting in a Titleist 3w and bought it because it was so darn good! I think it was a K series, and that was my first Titleist club that I bought and owned. A few years later, the next thing I tried was the 716 CB that I really loved and still own and play once in a while when I'm striking the ball well. But since the AP3 came around, even though it took me a year to get fitted correctly, I've never been happier with a set of irons.
Much like you and many others, I am dying to try a set of T200, and that may just happen for me- Great looking club!!

AP3 718 since they came out bout time to update