Replacing TF Ti Irons

[Pirate]

Hi, I picked up an ex-demo set of Top Flite Ti Tour Irons with reg graphite muscle shafts around 16 years ago.  They replaced a set of Ping Eye2 steel shaft clubs that I'd never been happy with.  I have played the Ti's 1-2 times a week ever since and enjoyed good consistent performance.  I am 56 years old playing off 14.  I always planned to replace them once one of the graphite shaft cracked, but these things are indestructible. My question is should I be looking to upgrade?  I have friends who change their clubs every couple of years and swear they can feel an improvement in ball striking - although I don't necessarily see any lower scores.  I don't think we've seen the revolutionary changes in iron head design that we've seem with woods and drivers but shaft technology must have improved massively since the bubble and muscle shafts days.

Any advice would be welcome as I am starting to play more these days and would love to get into single figures.