I did a flight many years ago in a ASW-20 in the spring. The "normal" checks said everything was fine.
Crossing 200' on tow, nothing added up.
Result was a mouse chewed hole in a TE probe tubing.
It was a 3hr flight, mostly seat of the pants and sound.
No ASI, no vario.......

While I have not had an electrical failure, it's nice to have a mechanical vario.
Yes, I really miss the audio, but for fun flying, butt vario and a mechanical gauge is good enough.
Yes, this is in eastern US, so not major issues with wave or ridge.

BTW, my first audio vario was a Development vario from Cambridge ( yes, Raouf Ismail) from when I crewed for him in Elmira. It was in SGS-1-26 SN 002 for many years. I still have the paperwork for it, we still have it.
Gosh, I have loved an audio vario since then.

And as others have stated, a paper map and mechanical instruments may get you home.......at least....in the eastern US. Not sure about the mountains in the west.