Anyhoo, my main takeaway lesson, from this and the "phantom disk" thread, is to beware of false economy.

I had a decent Plex server running for 3 to 4 years using >10 yo bits which was fine. However, when this started to go wrong, penny-pinching made me invest in a large number of ineffective remedies to try and rescue what I had. I now have a decent Plex server on a modern(ish) AM4 board with a Ryzen 3, 16GB of DDR4, enough disk space for the time being, and a new (very old design) Coolermaster case. This should last a while. The downside is that the ancient case design means that the cabling is a total rat's nest. Plus I have a semi-operational SATA card and no obvious way to expand.

If I'd just bitten the bullet straight away, I could have bought something like the much better MSI PRO B550M-VC WiFi motherboards, which has 8 SATA ports and 2 M2 slots, all of which can be used, and a fabulous case like a Fractal Design Meshify 2. When I include things like cables, brackets, case fans (included with the Fractal Design case) etc etc , I'd probably still have change from what I spent.

*Also, I wouldn't have tried to cram everything into the original case, causing a plastic tab to snap off one the SATA drive data connectors so that I now have one drive with a cable that has to stay in place and not be knocked or shaken or the drive stops working!

Go laser. Colour lasers are a reasonable price these days.
Won't get away from the connection issues (though getting network printer might help), but god they're better. Toners don't dry out from infrequent printing. Just run and run.

It's a thought. They look as though they're getting better at photo-prints as well, although from what I've seen they can be a pain to set up for this. But most of our printing is documents anyway.

I fairly recently got a "broken" Brother B&W laser printer off Facebook marketplace for free. Owner said they couldn't connect over Bluetooth/WiFi, app didn't work, cable wouldn't connect.

A quick search told me it wasn't a smart printer in any way shape or form, so attempting a wireless connection was a pointless endeavour anyway.

USB socket was bollocksed. Removed that and soldered an old cable directly to the PCB and it's running perfectly now.

I did buy some replacement USB sockets but that would mean taking it apart again, and my bodge job with the cable is still working. So they're in a drawer waiting to never be used.

Free is the charm as they say. 

I used to do the occasional soldering repair, but recently when I've tried on a couple of components I made a total bollocks of it. I don't know whether it's because I'm older and less "steady of hand" than I was, or the soldering stuff is different, or just that it's a skill you need to keep practicing.

I recently accidentally buggered a 3TB HDD by snapping of the little plastic tab over the data port. Lost the tab somewhere in the mess of my desk. I took an old 120GB donor drive and cut the matching tab off. This is nearly impossible to hold over the flapping pins while pushing a cable on, but it can be inserted into the female cable and then this is wiggled over the pins to make a decent contact. The cable is then glued in place with a hot glue gun. I know that I can make a "proper" repair by swapping the whole HDD circuit board (it's only held on with screws) with a matching donor board with intact SATA connectors. With this HDD, as with most, there's a BIOS chip which has to be desoldered from the original and used to replace the donor BIOS chip. 

1) my recent inability to solder, even though this is a really simple hot-air and flux job is a real blocker. 2) that people have cottoned-on to how straightforward this repair is (for all kinds of issues not just clumsy twats like me) and crappy old circuit boards are being ripped off dead disks and ebayed for silly money, doesn't help 3) but mainly the fact that my bodgy fix works, has stopped me seriously considering this.

The profit (your cost) is in the consumables, the printers are sold below cost.