A 1977 Fender won't have an original nitro paintjob. Check inside the neck pocket for any clues that indicate whether it has been refinished already. If you can determine that the current finish is not original, stripping it off and redoing it won't lose any value.
I'd probably leave the bridge alone, but I have had success improving old hardware with peek metal polish and elbow grease.
The chip in the pickguard is very common with musicmasters - I have a couple of 1972 musicmasters and the original pickguards both have cracks in this area. You can get a replacement pickguard made fairly inexpensively. earlpilanz on ebay should be able to sort you out if you send him the original guard or a tracing. You can always put the original one back on later so it won't affect the resale value.
I would replace the non-original screws with Fender vintage-style ones. You may need to wedge a bit of wooden cocktail stick in the holes to get the new screws to bite if the existing screws were oversized.
I don't know about filling the checking with superglue. It might work; maybe try a small area on the back first.