I preemptively replaced my water system this spring (electric to gas heater, added water softener). Took me a whole week (5-10pm work) and lots of pre-planning, but every time I walk downstairs I can't help but admire all the coppers lines I piped in. I dunno it was kinda like Hello World of the building trades, hearing the heater kick in after all was done was awesome.
Now, I've worked with my hands my whole life and have done tons of smallerish projects around this house, but this was the biggest one I tackled. Saved me 3-5k I'm sure and it really gave me a sense of accomplishment.
To each is own though.