Just saw a link on another forum that Miller Motorsports Park was closing:
Miller Motorsports Park Will Shut Down This Year On October 31.
The link didn't specifically address what would happen to the museum. I went out there in '13 and was blown away with all the Shelby stuff. Numerous Cobras, engines, memorabilia, a Daytona Coupe, one of each of the GT40s series and a ton of other stuff. I saw the Shelby museum in Denver and the Miller museum on the same trip a couple of weeks apart and considered the Miller museum to be superior.
All to say, if you get the opportunity to see it before it closes, be sure and take it.