Imports are generally the way to go on most games, especially since they use normal jewel cases.
Depends on the game. Obviously games where you don't care about story you can grab the japanese versions. But Panzer Dragoon is worth getting in english. And while Panzer Dragoon Saga is pricey, you can always sell it and at least break even. A huge reason for playing all four games is the atmosphere and story.
Guardian Heroes is not worth the asking price, same with Radiant Silvergun, just get a 360 and play those two on XBLA.
Daytona, Virtua Fighter 2 are both cheap and fun.
I've never been a huge street fighter fan, but everyone I know that is, swears by the Saturn versions.
Shining Force 3 is fun, but I'd just play that in emulation so you can get the english patches to the other two scenarios, and actually have the save come over properly.
Magic Knight Rayearth is not worth the price, its an OK adventure, but... not worth more than $30.
FWIW: Langrisser IV for Saturn is considered the best in the series, but... you might want to check el sallia to see if they have the translated script for it. (They translated the Playstation version)