I am also in the camp of if it ain’t broke don’t fix it but for me its more a matter do I want to be able to run it with other engines on the same track. I have upgraded quite a few myself but only dead MTH engines. My lone working PS1 remains original. The kits are designed to upgrade MTH engines so not a lot of modifications are required to install them and the instructions are pretty clear. You might want to try one yourself when the kits become available again.
Pete