Honestly i hate the idea of "repasting" as maintenance. People kill so much hardware doing this... Also there is so much more to it than just thermal conductivity and manufacturers often chose thermal interface based on many factors, like longevity and consistency of application. Thermal conductivity from specs is practically useless for judging how well it will work since it can be measured in different ways and there are different other factors which affect heat transfer.
I've seen 20 year old thermal interface in some servers and some videocards which was still in great condition and changing it did not improve things, except i am sure thermal compound i've used will not last 20 years...
Then there is the issue that there is a lot of randomness involved - it can be clearly observed on modern high power GPUs with bare die and ability to see hotspot temperature. You apply new fancy thermal compound, "GPU temperature" is a few C down, but suddenly hotspot is 20C higher. You remove it, reapply again the same way, and suddenly it is fine. You simply would not know this on older card with no ability to see hotspot temperature and then it'll fail some time later for unknown reason while being seemingly kept cool. A lot of effort goes into preventing this from the factory.
So i personally prefer to change thermal interface only if there is some indication it is needed. Like temperature increase over time, or being excessively old, like from 90s, with unknown history.
I also, for some unknown and seemingly illogical reason, dislike Thermal Grizzly. Something just feels... wrong. Too aggressive marketing (sponsoring every youtuber in existence), obscene prices, obvious signs of trying to get every bit of perceived performance at any cost. Most comparable to charging li-ion batteries to higher limit of what's possible without them exploding instead of normal voltage, which a lot of manufacturers used to do a lot and some still do. +5% capacity, 10x worse longevity, but if it allows better scores in reviews - anything goes. After all reviews never show anything related to longevity.
What i've wanted to try for a while is MX-6, higher viscosity is a good thing, should make it last longer in practice.