This is a good point, and applicable to my situation: I feel like my iron play has improved (over the past what just happens to be 5 years since I started playing) a lot and am at the point where I "want" - not necessarily "need" - an upgrade.
In my case, am looking to switch from R9s - which are great and I love them, and could keep playing with them - into the new Apex CF 16s. So from a GI set into a forged 'player' .. or sometimes classed cross-over GI/Player... But plz note I did make a few trips to two different stores and spent lots of time hitting several different makes and models, and hitting them alongside my current R9.
* Bottom Line:
IMHO, replace clubs based on your particular playing factors (and propensity to splurge), and _not_ on a calendar schedule.
AND - go to a store, or demo days if you can, and definitely test test test a number of different models.