Welcome to the forums!
The answer to your question would depend on how rare your particular trailer model might be, and what you
want to do with it!
If a trailer is rare it has significant collector value, which modifications would reduce. But they made quite a few Overlanders, so my guess is that your 1972 model is not very rare. So modifications won't hurt the resale value much if any--and if you fixed something that didn't work, of course, you added to the value.
I agree with the above Isuzusweet--CLEAN the heck out of everything before deciding what you want to do about painting and refinishing. I think your 1972 still had the Zolatone paint interior, which is indestructable. You can clean it with anything, up to scouring powder. When we got our 1960
Pacer (years ago) the inside was a dingy yellow. My wife scrubbed it two or three times with some kind of dynamite cleaner (Simple Green, if I recall) and it cleaned up good as new.
We faced the same question with our 1960--on the one hand, we wanted more creature comforts--the Pacer was pretty Spartan--but we didn't want to butcher up the nearly original trailer because 1960
rare--they only made 100 of them. So we ended up buying a 1980 trailer that had the things we wanted and sold the Pacer to someone who wanted a rare one.
When we first started Airstreaming (13 years ago now) an experinced trailer restorer said, "Clean it up and fix it up until it's roadworthy and habitable, then take it on the road." That was excellent advice. When you camp in an Airstream for a while you will find things you want, but you will also discover that some of the features were made that way for very good reasons. Your ideas about modifications will evolve as you use the trailer.