Btw, about limiting magic... it could be a good idea to limit some magic types or levels on some (not very common) types of terrain, etc. Uhm, let's say, something similar to "cursed ground" in HMM games - in HMM you can't cast anything (except very few basic spells) when fighting on "cursed ground" terrain, this virtually eliminates magic usage (due to lack of useful spells to cast) and does not looks artificial, etc. Also, it could be a good idea to create few "opposite" areas where "magic flows in the air" so wizards can cast magic more efficiently and/or at reduced costs in such areas (let's say, double efficiency, etc). These could be for example, some areas nearly mana seed, etc (where magic should flow in the air for sure).
Do not know if these ideas are stupid or maybe too hard to implement. I guess it could be fairly easy to implement such system as server-side scripts in way similar to some already existing spells checking their coordinates + some tilesets reflecting special areas, but I have no idea if this will harm server performance, etc.
P.S. yes, I got some very basic ideas on how magic handled right now by eAthena. I was constantly failing on some quest for a numerous tries (old tree in a desert) and this forced me to look into server-side sources to check if my actions were correct and I'm doing things properly for the quest and what's the hell is going on, as some kind of last resort. Btw, devs may want to see bug 733 in bug tracker, it has been marked as "private" by me for some reasons and all this mess caused me to try to "use source, Luke" after many fruitless attempts to complete quest by fair means
(and as extra bonus I has figured out that I tried to do right things as well as that magic could be sensitive to it's coordinates, though I never managed to see how this works, probably due to lack of luck in spellcasting and some excessive luck in getting weird issues reported in the bug 733).