Hello,
I am a union pipefitter/house hacker from the Twin Cities, and I have some advise:
1.) Old galvanized is easy to rip out and replace with pex. Most houses only have a kitchen, bathroom, and laundry to replace. It is cheap and easy.
2.) Old Electrical is a no go for me. Though if you do buy an older home, replace the wiring. Most old house have the plaster walls. If you would like to keep the plaster, use the old electrical as a cable pull for your new electrical. It will save you from having to open up your walls.
3.) There is nothing wrong with old HVAC. With old forced-air systems, you run into asbestos tape, runs coming off the trunk that aren't sized or balanced for the house. There are a lot of fly by night scabs out there who do not Manual D or Manual J a job.
You also want to check for dirty filters. In older (low efficiency) systems you do not really need to worry about seeing a dirty filter, but in the newer high efficiency you do. They incorporate a secondary heat exchanger (much like an Evaporators A-Coil) that has less space between the fins. With prolonged use of a dirty filter, ducts or no filter; it can become clogged.