As I've mentioned before, months ago I gave him the Super Powers' Hall of Justice playset I owned as a kid. This cool playset has become the house of heroes while the Batcave we found at the flea market is always the hideout for villains.
Whenever we play with our Star Wars collection these two playsets are used. You can see that the Hall of Justice is the perfect thing for the Jedi council to hold meeting and spend too much time talking and not taking actions (like in the prequel films). While on the other side the classic original trilogy Star Wars figures are ready for action!
The Batcave is almost the perfect faux Death Star playset. There's traps, a weird rotative room (carbonite freezing usually happens there), a seat for the Emperor and a big door for Jabba the Hutt to be able to actually enter.
That night the Imaginext's dinosaurs we own were used as Rancor monsters while Darth Vader was lucky enough to drive the Batmobile. That's how I spend most of my nights with my incredible three years old son.