Well, the adjustments and lube should be done regularly. (of course) When you do this, the bike is up on the rear stand. As you rotate the rear tire manually, you will noticed "tight" spots and "loose" spot, these are caused by chain wear. If you have excessiveness (this can be subjective) with this type of condition, you should change the chain. Say you have one tight spot, you can adjust that out, but more than that, I think it's advisable to think about replacement. Also, look for "kinks" in the chain. If you start to see those, it's probably time to bin the chain as well.
I'm sure others have their opinion on the subject.
Also, it's advisable to go more on the loose side with the chain adjustment, because a tight chain can actually limit your suspension, and this can result in breakage under stress.
We;ve used various aged chains with various aged sprockets, but that's just the nature of budget racing.