I'd fix the door sag, because that's relatively easy and is very noticeable to the buyer. I'd also fix the EGR because buyers in some states can't register a car if it has a CEL. I learned that selling my Beetle TDI. Also, check engine lights turn off buyers because there's the fear of "what else is wrong with that black box?" You're up north, so the A/C isn't as much of an issue, but down south it would be a deal-breaker. The rust is what it is, and depending on the buyer can be overlooked.
