Getting into my mid 60's and climbing hills and mountains isn't getting any easier. I'm going to replace my drivetrain, starting with my crankset, going from a 53-39 to a 50-34 (and the rear with a 12-30). My CF bike has probably 20,000-25,000 miles on it. No problems with the BB but since I'm doing the crankset, do you recommend getting a new BB?

You may have no choice. Unless the replacement crank and the old crank share the same model and size bottom bracket, the new crank will dictate what bottom bracket it requires.

Changing from a racing double to a compact double is a smart move. Most riders have very little use for a 53-12 compared to the practical value of lower climbing gears. I'm even building up a bike with a "sub-compact" double - 42/26 or 42/28.

What kind of crankset and BB does your bike currently have? Cranksets can use different bottom brackets to get proper road chainline. This is especially true in the square taper world.
But if your current BB puts the new crank in the proper positioning, and bearings still are smooth, I'd stick with the old BB. The bearings wearing out won't damage the bike, whether in a cartridge unit (square taper or Octalink/splined) or external-bearings.

Also you may want to check your derailler capacity for the bigger rear cassette

Replacing a threaded or press fit BB is $20-$30 bucks (for a good one). I would go ahead and replace it.

Thanks for the input guys. AT that price it makes sense to get a new BB. All my setup is 10 speed Ultegra, I'll go with SM-BBR60.

Now with the latest external bearing cranks the spindle is a tube fixed to the crank arm..
getting the whole thing at once in the box will be a $aving$ ..