Also disk space - i don't want to keep 500 MB of failed login attempts just to have a week of syslog available.

Rotate your logs bud.

Also, suppressing these logs is the same as rapidly rotating new logs.

It is not. Deleting my spam folder is not the same as deleting yesterdays email.

Rotating only splits the data up into N files, not make it consume less space for a week of logs.

logrotate compresses logs.

A Gameboy would probably have the computing resources to do a thousand such calculations a millisecond.