My opinion based on my experience.
Bought the 80 series about 8 years ago with 260k on the clock. Put the turbo on at 330k, cost about 4k including a 2.5" exhaust. Now nudging 400k and not a problem. We get 12 l/100km not towing, 16 l/100kn towing the KK. Most of the work it does is towing. Have spoken to my mechanic lots about updating, but he says if you know the service history and maintain it well, it is not worth updating. I have also spent a great deal of time and a little money in personalising (drawers, fridge slide, winch, cameras, electric brakes, dual batteries, lift kit, air bags, driving lights, pack rack). All these extras make it an expensive exercise to upgrade and replace all the extras.
If you have a sound unit to start with, I believe it is worth spending the money to fix rather than replace.