On one hand, it is clearly going to be harder for a random zombie machine to find your ssh on a non-standard port that requires knocking and a particular less usual username.
On the other hand, you're breaking from your distribution's standard installation. You increase the risk of breaking on a future upgrade. You could lock yourself out, perhaps, and there's a cost associated with this. In the worst case a distribution upgrade will fix a security hole and you'll be left with it (say for example because you modded the config file, dpkg queried it, you rushed through the prompts and it got left alone).
I accept my scenario is unlikely, but it is also unlikely that someone will crack your up-to-date machine using distribution standard ssh, a secure root password and public keys for day-to-day access.
It is far more likely that someone will access your secure machine from an insecure place with a keylogger running and get cracked that way.