It's worth a look if you are going to a race event there (some face events offer free museum entry). Take a look on trip advisor for a range of views. Here's another site with similar offer https://www.mailexperiences.co.uk/visit-to-donington-grand-prix-collection-sp1 As for the comment about military vehicles, erm well... Just Google Tom Wheatcroft Nazi collection and you will soon realise.
Never been, is it worth while trek up there? Be around 1.5/2 hour drive. Is it relatively large or can you breeze through in 20 minutes?
There's a minimum £2.49 delivery charge, and you can get two adult tickets for £12 (code doesn't work for that one unfortunately).
Sounds great (y)