Drive shaft bearing and rubber are usually replaced incidentally when a U-joint goes bad, which happens randomly based on how you drive. If you're on all-original U-joints at 250k, you must be a very gentle driver... Anyway, don't worry about the center bearing, it will greatly outlast the u-joints, so just do it next time your U-joints get noisy. Doing all three joints plus bearing and rubber only takes marginally longer than doing one joint. So when the time comes that you've got to do one, you might as well do the whole job.

Rear wheel bearings usually go bad at every ice age, though some people like to preventively replace them every few thousand years. I've got over 400k on my originals, and I'm planning on doing them whenever I overhaul the rear end, which is happening, ah, sometime. Anyway, we're not headed for an ice age anytime soon so if I were you I'd ignore the rear wheel bearings and worry about something else.