Hi Joe:
I'm a life-long Spitfire admirer too. Based on my experience, the RAF Museum is an "absolutely must see" spot. I made the mistake of allowing myself to be "booked" so as to allow me only an afternoon on-site. It was totally inadequate, as I was litterally running from exhibit to exhibit.
The next year I gave myself an entire day to visit. Much better, as I arrived within a few minutes of door opening, and stayed until they almost had to drag me out of the facility. I think you really need 2 days to see everything, talk to people, and generally absorb the significance of what's under the roof.
You'll also want to buy a few keepsakes in the gift shop, so save a ltlle time and money for that.
One of the things I notice about the British museums in general is the high quality of the restorations and the care taken to ensure that somebody can't damage or vandalize the displays. It means though, that you'll spend a fair amount of time standing there in the crowd of the non-aviation types wanting to climb the barrier and hop into the cockpit.
I had the unfortunate experience of attending the USAF Museum in Dayton a few years ago. Marvellous place, full of history. I had the chance to lay hands on one of the X-15's that had contributed so much to the science of highspeed flight. As I was marvelling about the way it was built, I noticed some love crazed juvenile couple had carved their initials inside a heart just below the canopy ..... what jerks!
Enjoy your visit.
Regards,
Fogducker