I have tried to save money on headsets many times, but always wind up regretting it. A failing or crappy headset is not immediately obvious. The handling of the bike gets subtly worse, feels twitchy, or like "pushing with a rope" as I like to put it, especially as you are limping home exhausted after a long ride. This being said, there are many mid range headsets available these days that are excellent, if you don't need great weather sealing. I use high polish CC 110 on my best bike, which sees weather. Gave up on KK as overpriced ugly logos.

Bottom bracket? Seals, maybe slightly more efficiency under heavy loads on my SKF with its large balls, and will never need to be serviced, ever. But yes, you could replace cheap ones every other year for decades and come out ahead. We do have a disposable society, after all.

Worth it? Well... what else are you going to spend your money on?