Technically, there were more SW models in Episode I than in any of the OT, but you're right, the explosions are all CG. I know they filmed models of the N-1 Naboo starfighters blowing up because I've seen videos of it, but in the final film I'm pretty sure they used CG explsions for all, or at least almost all. Beyond that, there really isn't any examples in the PT of dogfights where ships explode--the land battles used some real pyro elements, but they are comped in totally CG landscapes and totally CG vehicles, so it doesn't look like real elements anyway. The ROTS opening spacefight, as far as I am aware, was a 100% CG affair.