I have about the same dryer I’ve been keeping alive for years. I wouldn’t worry too much about the dull spot. That’s likely where the old coil got a hot spot before it failed. It’s just discolored the zinc coating. Shouldn’t effect heat dissipation but it might be more susceptible to rust now.
If you’re not in a big hurry, I would replace that white plastic bearing the drum rides on (you can see it on the very left in the last picture). It’s super squeaky when it fails. If you don’t replace it, at least give it a dollop of high temp grease.