I tested on some NAS (Qnap and Synology). Is not a real overkill if you have 8GB RAM. If you have less I would recommend to use it as backup for your bitcoin blockchain.

I use it like that now on a Qnap NAS with 4GB RAM and 2 disks in RAID. Is syncing all the time the blockchain and I just keep it as a copy and occasionally as neutrino node.

When you setup a new node in the LAN, you just have to point your new node to sync from your local NAS node. Is faster. You can also use it to just raw copy the blockchain data if you like, but then your new node will take anyways a while to create the index of those blocks. Up to you which method you want.

But important is that you can have at hand anytime a local copy of the blockchain and a node up and running, just in case.

I would not run a Electrum / Fulcrum server and a LN node on the same NAS, will be too much, indeed. But a simple bitcoin node syncing is OK.

Apart from that, yes, is very useful for your personal files, like a personal cloud. I use it also to sync all my mobile wallets and other nodes, straight to the NAS.

I don't like to mix too much a full LN node with other stuff.