I saw a video of a guy buying a bluetooth amp with a twist-knob on/off and just gluing it into the guts of his old radio. While I like this idea - and especially it's DIY nature - I do think that it would be annoying only having a semi-functioning radio. At that point, better to just attach the knob somewhere else and put something useful in the radio slot.
I could buy a classic-looking radio. These seem to vary from many hundreds of pounds to not very much at all. I assume the name-brand options won't fall apart as quickly but who really knows.
This one from Amazon seems to be well reviewed, and has a good suite of buttons/features. Perhaps I'll replace my current setup with that. It looks to be shorter than a standard single DIN radio, so it presumably would also free up some space in the back. The only issue would be the re-wiring that would inevitably be required. I do not fancy doing that...
Might also be good from a lack of battery drainage perspective?