I always go in to a new air/naval museum knowing at the outset that they are kneecapped by how much funding they have to work with. You can get some pretty nice results working with basically nothing, but that only takes you so far. That said:

• Lighting. As others have said, I like to be able to see the exhibits, and the older I get, the better the lighting needs to be. Overhead banks of blinding fluorescents are not my first choice, but are far better than a few dim spotlights.
• Proximity. I don’t need to touch it, but the difference between 5 feet away and 50 feet away is enormous. Up close you can drink in as much detail as your brain can process. Being able to step back to take in the totality of the aircraft is a bonus.
• Information. I like to know what I’m looking at, and OK, am probably one of the few who reads every word of information presented instead of just skimming the headline. I want at least the basic details on the airframe I’m looking at, and a capsule history at minimum. More information is always better, for those who want it.
• Benches. Some place to sit, preferably where I can gaze in silent wonder at these magnificent machines. The older you get, the more important benches or chairs is.