For that, you'd have to actually edit the game's internal files - which can be done with a BDAT editor, since the most important files are in common.bdat.Is it possible to increase the value of SP and WP gained each time? I couldn't find a place for that in the save editor nor any cheat codes that do that, only for experience.
This data dump is a fantastic resource - to edit an enemy's WP/SP yield, once you've dumped the files and gotten everything set up (tutorial), go to CHR_EnArrange, and use the dump to locate the enemy's name and numerical ID, to go to the correct line in the BDAT editor. Then you should see "EXPRev", "GoldRev", "WPRev" and "SPRev", which are how much of each thing that enemy rewards.