Overpainting Diecast?

I have repainted many diecasts and always I took the car completely apart and stripped all the old paint off the body (using a normal householder stripper which generally takes a couple of hours from start to finish), filled in any imperfections, primed and painted.

I agree with Hans, strip it. I use any paint stripper from the hardware store on diecast an overnight will usually do it. As Hans said, only the metal!
You always run the risk of non-compatible paint when painting over (lacquer paint eats a lot of others) and you also lose detail just overpainting.

Dave,
although i have no experience overpainting Revell models,i think i can tell you what i do in a case like this.
i haven't gotten any good results with the what you proposed on my Code 3 ,Corgi and Burago models.(i got the broken paint effect (craqeully?effect) B/C the paints didn't like eacht other)
i put the metal (just the metal!!!,no plastics)mostly in non acetone nail remover or thinner and wait a couple of days for the paint to get off.
i make it fat free and give it it's first base coat.
i use Revell base spray paint and tamiya red and black.
Hnas

I've painted a couple of die cast kits, I just lightly sanded to scuff the surface up then primered over it and painted like I normally do.