Well, I do many dives in the 60-70M range and I still never spend more than 10-15 minutes at those depths. Most of my dive is spent above 50M, so I pick my exposure protection for the part of the dive I spend the most time in.
In Komodo off season, I hit a bottom temp of 62F at 110ft, very cold to be sure. But I was only there for 10 minutes, so the 3MM suit was fine...and the diving was unexpectedly exceptional. Am I going to change my suit and weights around for every dive in which I might hit a thermocline? No, it's just plain unsafe to mess around with your bouyancy and mobility just to try and make yourself more comfortable for those few minutes.
I can easily tough it out for a few cold minutes and I value the familiarity, ease of movement and general comfort of diving with less weights and a thinner suit, much more than I do being a little shivery for a few minutes...