You can simply pipe top's output to a file using something like cron. There is a very good tool for boot times though integrated into systemd. Call it using `systemd-analyze`. It has a lot of subcommands you can check by `systemd-analyze --help`.

Also, if you'd like to compare performance degradation over time, NixOS is a good choice to run because it can simply rollback to old configurations and you can see what changed.

If you could give me a brief list of what features you expect from such a tool I'll be happy to take it up as a project and release it.

Don't reinvent collectd :)

Thanks for the recommendation. Exactly what the parent commenter was asking for.

Yup, thanks, collectd seems to be exactly what I was looking for.