It's perfectly acceptable to do what ever it takes to keep a vintage instrument playing provided that the repair and/or action is appropriate for the instrument.
In this case although this is a vintage instrument maintaining functionality won't hurt it's value and IME may even enhance it's value since it's currently not important enough to be more valuable as a wall hanger than a player.
More specifically if the fret plane needs to be redone carefully remove frets, level the board and refret and EVO is not only fine it's a great choice IME. The work should be done by a professional though if you are really concerned with not harming the value. A new nut will likely need to be fashioned as well since fret height may increase if not and if the old nut is working well that's OK too. Of course a precision set-up follows, servicing the electronics, etc.
Regarding the heel separation I would not use any filler or attempt any "masking" repair. There is WAY too much of that in the vintage guitar world and these repairs only serve to attempt, often very poorly.... to cover-up an issue actually making the issue seem possibly more serious than it actually is. If the neck is stable, angle OK the separation should be either properly repaired with a full-on, professional neck reset or left alone. My vote is if it ain't broke, and it's really not, leave it alone.
Check out our home page for some pics of a 50's Gretch that Dave just finished removing the frets and refretting with EVO and he made a new Bixsby tail piece bracket and saddle as well. A killer cool guitar it is and one of the few that come our way that I actually would like to have.
Regarding my comments on who does the work. First no offense intended, I have no idea what your experience level is. If you are a pro go for it but most pros would not be asking these questions. Second don't look at us my comments are generic in nature, intended to help you and we don't accept shipped in work, ever. We are far too busy to be in the slipping and deceiving business...
Lastly if protecting the value of the instrument is high on your list who does the repair can play into that. We are often asked up front if once we do the work if our name can be referenced as the ones who did the work to prospective buyers. Although we hate getting involved in private sales it happens from time to time especially with pre-war Martins and occasionally Les Paul's, original ones or instruments that were owned by someone famous. Having a pro do the work brings some level of comfort to prospective buyers at times, not always.
Good luck to ya.
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But I don't think it will ruin anything. IT comes in various colors including mahogany.