I don't know about the specifics of your situation, but in general yes, heat can affect burn quality. Usually an overheated drive will do worse than one that is properly cooled. And burning (even reading) discs does generate heat within a drive, so the more you use a drive the hotter it tends to get.
You might try reconfiguring your drive bay configuration and making sure the burner is getting sufficient cooling.
The bad burns I'm getting are either higher C2 errors or complete failures (i.e. red blocks on Scan Disk). Sometimes I actually fail to burn with an error like "lost tracking".
BTW, I did replace my dead rear case fan with a quieter one and it did increase my MB temperatures. If the problem is the motor heating up and not the laser, perhaps I can speed up my front case fans to see if it helps.
Should reviews do this kind of "stress" testing? CD-RW's could be used to keep costs down. The idea is similar to the CPU overclock tests like Prime95. I know the LiteOn is cheaper than a Plextor, but is this the difference? Are better drives "heavier duty"?
A sample test would go through 10 burns to see if the performance degrades.
Heat does cause drive failure, and can cause higher error rates, but I'm not sure that your problem is related to heat. Usually it would get worse with use, not better. I can't really think of a reason why you would see decreasing error rates unless the drive is burning slower.