Yes, I still have my MP3 collection as well my fansub anime collection from way back when I was more active in that scene. Nowadays I somewhat keep up with fansubbing, but it's mostly my nephews and nieces that watch it now after I curate each series.I'm in the same boat with streaming today. I still have most of my back in the day super large mp3 collection on 2x 500gb ext drives that I haven't powered on in years now. :0 I do probably need to move that data into the fold if I want to keep it. Now that I think about it, I've got a lot of data like that to archive.
You're dead-on about a secondary nas being older gear; and in fact, it can be nearly ridiculous since you'll never even get 480Mbps to the drive over most Internet connections. (I'm watching a copy job right now running at 3Mbps on a link that's got 50Mbps on the upload side and 500Mbps on the download side--there's just so much overhead.) You can literally just buy one of these external drives and plug it into the usb port on some consumer router that can handle the size and you've got a dead cheap offsite backup.
If you don't want to pay for synlogy dsm, there is the xpenology that you can run on your own hardware. If your dad is connecting storage directly to his laptop, isn't that DAS (direct attached storage)?
My backup NAS is running old gear that I already had, but I'm considering building a new backup NAS using an Atom C3000 platform. The benefit here is that it won't use as much power. The processing power is kind of pokey but it probably won't matter as long as it can reliably push a gigabit connection, which it should have no problem doing. It's come down to mostly chassis selection and willpower to do it though.
My dad was technical for back in the mainframe days. He knows his way around modern hardware but isn't techy in today's sense. He still turns off stuff he doesn't use, and doesn't like the idea of a computer running 24/7 using power. A QNAP box though, won him over since it's an "appliance," hah. Certain QNAP models support concurrent DAS mode over Thunderbolt. I set him up with a TVS-872XT with the CPU upgraded to a i7 8700T and 32 GB DDR4.