Probably not, since it's a home NAS the reads won't be very repeatable. I wanted to prevent the hard disks from waking up, but it's mostly writes, so it doesn't help there either.

Add the SSD to its own pool, set up as a working share, then use a utility or script to sync contents a few times a day?

That would probably be easier, yep, thanks. It's more straightforward to just make a partition on it and rsync twice a day.