Upload & Sell: Off
You do not need to back up the caches as they are readily - but slowly - rebuilt at any time. The issue is whether the extra time it takes every time you back up outweighs the time you save if / when you have to recover from a backup. I'd say not, unless you have a flaky computer.
Occasionally I have had troubles with recovering preview data correctly but it happens so inconsistently that I have not established why it happens. When it does occur the previews need to be rebuilt anyway and the recovered backup is largely useless.
btw, my computer has been very flaky for several months and I backup very often to multiple external drives - so often that it is not worthwhile backing up tens of GB of Lr previews and ACR cache.
I set Lr to backup the catalog every time it shuts down but sometimes I shut it down manually to force a fresh backup even though I want to do more work. Those backups are only on the internal drive because I do not keep external drives connected unnecessarily, but they're all sent to an external drive within a few days (sooner if I do a lot of work in Lr) when I do a general backup. When I've made at least two external backups onto physically separate drives I will delete most of the Lr backups that are on the internal drive.
I rely on my Lr catalog a lot because I do not use .xmp files. That is because when I use external software such as from camera manufacturers it does not respect the .xmp files. Even so, I do as much as possible of any file relocation, renaming, etc., within Lr.
My experience suggests that having too few backups is far worse than having too many. Even my backup drives die on me.
The ACR cache holds partially-converted raw files. Depending on how many separate raw files you process in develop module and how often and how fast, that cache will either be huge or will not contain all of the image files you need and so maintaining a backup is not convenient and is certainly not critical. New ACR cache data will be built as and when you open a raw file if it is not already in the cache.
The Lr preview cache can easily be rebuilt overnight any time it is needed. That might be because you lost the old cache in a drive failure or because you have changed default settings in Lr and want the previews updated. Either way, having a backup is not critical. It will be no good if it is out of date.
In case you have not considered it, there is a great advantage in Lr to have all of your image files under a single parent folder so that if you need to access your backups at any time - even on a different drive letter from the original location - you can very quickly find missing files for any one image folder and it will automatically find the rest. If the folders are separated in the catalog by not sharing a common parent folder then Lr needs you to find them separately. This issue may never arise for you until you come to recover lost data from backups and at that stage you already have enough hassles on your plate.