Is the time required for incremental Time Machine backups greatly affected by the number of files? Is the time required for incremental Time Machine backups greatly affected by the number of files being backed up? I have a large number of files on my Mac that very rarely change and aren't "mission critical". If they greatly affect backup time I'll exclude them from Time Machine but if they don't I'll just backup everything. Backup size is a non-issue for me.

If it matters, I have Time Machine backing up to a remote box that is usually on the local network.
Incremental backups only backup what has changed. The number of unchanged files is irrelevant during an incremental backup. If you suddenly change all of the "large number of files", the next incremental backup will take significantly more time.