Have two balls that were drilled lefty originally and are now plugged and drilled righty.  Not a thing wrong w/them -- the nice thing about switch-overs is that the track area is virginal 93.725% of the time, so it's like getting a new ball for used ball price.  Since the 4 you mentioned are symmetricals, absolutely no problem whatsoever.  If they were true assymetricals, there might (depending on philosophy on mass bias importance) be a need to throw them on a determinator just to make sure the mass bias is still close to where it's marked.

Yes, their is a disadvantage.

Plugging does change the weights and core of the ball around. Plug is lighter than the rest of the ball.  Any part of the core that was drilled out by the first drill is being replaced with light material.  The core is not the same as in a new ball.

What's more important to me is the condition of the coverstock.  It just seems to me that all used balls people try to sell have "just a few games on it".  I'm too concerned the good days of the balls life are behind them when it comes time to plug and redrill the ball.  

It's a gamble.  You may get a good ball, cheaply.  It may be a piece of junk.  Personally, I've had success plugging MY equipment when I didn't like what the ball was doing and the new layout worked much better.  I've had mostly poor results drilling "bargains" that I've found.