To clarify, especially for readers like me who don't know what Psypoke is: You want a search engine for items, where players can enter their criteria and find all matching items? And maybe one for monsters, where players can enter a desired material and see which monsters drop it? Stuff like that?
It's a good idea. Our current system is basically like classic Yahoo --- a curated list. The new idea is like Google. Definitely more maintainable, once it's working.
I don't know anything about MediaWiki developer extensions. But basically you want something that can parse and index your infobox parameters? This could be done with external scripts written in Python, Perl, etc. But hopefully the developer extensions offer some shortcuts.