1) On one hand, the player/researcher is paying for the changes with time, money and DP.
a) Time for research is as rare as horses in my game (Adventuring is hard on mounts, apparently.) and trekking through tombs, forests, etc. leaves little time for study.
b) Money is also fairly scarce. Coinage isn't lying around and overall the group has no skill in appraisal or bartering. Exchange rates are also helpful for controlling disposable income.
c) DP is available at 100/lvl. You're still subject to penalties for developing more than 5 Lists/lvl, etc.
2) On the other, I might not fully consider how a mod impacts the game.
a) Allowing the Mage to take a few Monk Lists (Body Renewal) as Base makes him very self-sufficient. SM in the List compounds the problem. He's pretty successful at "caster/self to target/touch", which is only -30 SM. Smart player.
b) Also, the same guy has researched (adding a spell to known List) 4th lvl Presence (Essence Perceptions) to 50ft rad and 9th lvl to 10ft/lvl. Sure he paid for it, but it is vexing when the PC's believe someone is around the corner..
All spells in my game require SCSM and I don't use overcasting. Spell casting is dangerous business.
Thanks for the ideas. My players are getting crafty..