First a disclaimer - I know very little about footbed technology. I'm skiing some old cork ones fitted about 7 years ago.
But I do know that an adult foot does change over time (and this is especailly true for women - and very pronounced during after pregnacy).
And I'm always wary of salesmen who want to sell you new things.
I'm happy with my footbeds, as they do their job - namely get me in the proper position (I am slightly under-pronated) and keep my foot snug. I notice the breakdown in my boots over time, much more than any issues with the footbeds.
That being said - I bet the newer models are better, but you would have to be the judge. I will probably change mine when my spouse/kids start to complain about the magnitude of their odor...
Feet changing--depends on lots of factors; age, injury, what kind of work one does (are you on your feet alot). If the footbeds you have keep your feet supported as they did when they were made and seem structurally sound, why buy? If you have had any boot work recently, such as punching out the forefoot area, maybe that is a indication of foot shape changing?