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.