Here's an unscientific way to check the condition of wheel hubs without taking anything apart. With the wheel off the ground, give it a good spin. Mine keep spinning longer than two minutes. If it can do that silently and has no side-to-side play, the bearings are fine.

Headsets can be checked by raising the front wheel and seeing if the wheel falls to each side by its own weight, with no notchiness or tendency to remain straight ahead. With the wheel on the ground, engage the front brake and rock the bike forward. If the bearings are loose, you will sense movement.

A BB can be checked for looseness by wiggling the cranks side to side. Remove the chain from the ring(s) and spin the pedals to check for notchiness and rumbilng. This is not as good as removing the cranks and spinning the BB spindle with the fingertips, but it will reveal an obvious problem.

By doing these checks, you won't need to service bearings nearly as often as you should bathe.