My advice is: Find a plane which has the equipment you want and need. Don’t by too cheap or even expensive with old equipment. Narco radios are nice but they do not fly GPS approaches. I exchanged mine for Garmin radios 10 years ago. In my opinion, a good Waas GPS, an Aspen PFD or some other glass panel with a good autopilot shall be the basic equipment today. A good trransponder with ADSB in and out is also important.
Problem with the avionics is that it is very expensive to install. Especially with the old panels, most of the time you also have to rebuild the whole panel. So updating outdated avionics is always a very expensive task. The final costs and downtime are not really predictable.
I would not care so much about the interior. This is very psersonal and can be upgraded easily. You can even do some of the work yourself.
This is from my own experience.
I bought a M20F for a good price with outdated avionics, panel, interior. If I add up my investments for speed mods, avionics …. I could have easily bought a very well equipped J model and left additional money in the bank. My F flyes wonderfully and is not slower than most of the Js, but the upgrades took not only money, there was also downtime needed.