Generally this suggestion is really good. "adding two balls" isn't necessarily the right answer, tho. It just depends how they fit. It's no problem for the balls to rub against each other, because the grease film protects them if the grease is clean.
A second advantage is that the ball to race contact points are more random and occur over the entire bearing. With caged bearings you can get fixed contact and grinding as dirt accumulates, leading to faster wear.
You can't always solve BB problems by going to a sealed BB. For old Campy for example, Campy doesn't make sealed replacements for the NR and SR products (however, Phil Woods does). There was a wide range of spindle lengths in those loose spindle days, and they're not necessarily the same lengths as today. It's also not smart to replace NR/SR campy with Shimano BBs even if the lengths are the same, because the square ends are not the same, and the crank will not torque down to the same width. The tapers are also not the same, and the Shimano BB can overstress the Campy arms. So if you're running vintage Campy, you need to either stay original or be very careful.
Similar issues but probably worse with vintage Zeus or Stronglight, simply due to less availability of parts. Keep the old stuff working!