It's hard to say what cause of error is in particular, without a bit of troubleshooting. Where were these problem tracks downloaded from?
Have you tried all of the troubleshooting here?
Troubleshooting songs that skip on iP
Again, I"m not really all of this troubleshooting is worth it since as you stated the problem is only apparent on the older iPod Video, which would point to an issue with that device. You could try and do a disk diagnostic on it to see if there is anything in particular that stands out there. See this post from another forum member turingtest2 describing how to perform this test and what the numbers mean.
https://discussions.apple.com/thread/3784647?start=0&tstart=0
Apple doesn't have a trade in policy, but they do have a recyling program where you can bring your old iPod into be recycled for a 10% discoun towards the purchase of a new one.
B-rock