I love the Meryl Silverburgh approach to character reuse - crossovers are fun, shared universes are interesting when done well, but properly recycling a character to fit into a different universe with a new non-clashing personality and lore is just next-level.
...that said, i've also always had a soft spot for older characters becoming playable in newer titles somehow or other. like how gunvolt was added as an initially free update to blaster master zero, for instance. that's always pretty funky to see.