I have a mk4 golf with the ALH, it has 313k on the body and 341k on the engine and transmission, which is because the drivetrain outlived the Jetta wagon it came in. During the swap over it got a new timing belt, valve seals, and some general cleaning. I did swap in the larger injectors that came with the blown up engine in the Golf as well. I've been getting 40 mpg, which is low but I find it harder to keep my foot out of the plush cushion of torque it makes now...
Most of the electrical issues reputation come from two places: the design of the door latches and the coolant level sensor. The door latches have 4 micro switches in each on to detect open / close and locked / unlocked. When they fail, the car can become "possessed" as it gets confused about whether certain doors are locked / unlocked, etc. Early mk4s had a fault in the coolant level sensor that allowed coolant to wick up and through it, into the wiring. This caused horrific damage, and was a silent killer in that by the time you notice, it's too late. Revisions to the sensor / reservoir have basically fixed that. The Mk4s I've had have been quite electrically reliable on the whole. Rust has been a much bigger issue -- It's the rockers that will kill the car, clean behind the front fender liners and make sure they are not cracked. Pull some of the oval plugs and wash out the inside of the rockers, and spray with some cavity wax. Make sure the other body plugs in the vicinity are intact. I am in the rust belt though, so things might not be so dire in nicer climates.
I can't speak to the cam issue other than that I see plenty of other high mileage BEW cars out there. Other than that there aren't any issues that aren't worse than any other turbo gas car tbh, they're just different because diesel. The turbos and EGR can get clogged with soot, for instance -- the easiest way to avoid this is to get the car fully up to temp on the highway once a week or so. The intakes can clog up due to the EGR + crank case vent, but that get's taken care of on the order of magnitude of timing belts, and again is lessened by avoiding short trips. Mk4 TDIs have a good online forum presence, and there's lots of good information on maintenance and mods. You don't really need the manual for most jobs because they are so well documented.
For reference / comparison, my girlfriend has a Gen 3 Prius. It's a good car in a lot of ways -- it's more respectable than my old Golf to the majority of the population, it gets really good mileage around town, it comes up to temperature quickly in the winter, and the factory bluetooth stereo is better than the contraption I have. But, as the driving skews towards highway driving, I get similar mileage, and the Golf is a nicer car to drive long distances on the highway (the noise in the Prius is what gets me). Diesel prices have been really good this year, so the fuel costs per mile have been pretty close.The Golf has also been technically cheaper than going out and buying a comparable Prius (tbf, the Gen 3 is also 10 years newer), but the Prius has been cheaper in maintenance (the only really big money item I'd worry about would be the battery and the chassis rusting out). The Golf can tow a lot more than the Prius -- it will happily move more weight than I am comfortable putting behind it. Overall, a diesel car is a good fit for my driving needs right now because I am doing a lot of highway driving with minimal stop and go, along with using it to tow trailers and tug cars around. If that were to change to more non highway driving and traffic then the Prius would definitely be a better fit.
