1) you're thinking along the wrong lines
the main point is that the external mapper generates the important file that contains warp info for the server. thats all. as for screwing up external maps, well, if you md5 hash check them and redownload them if they're incorrect, then that helps
2) having the game non server side based would mean that then the game has to do more work also, plus a LOT more network lag and a LOT easier to heck :/
3) memory editing only works locally, so with a good server side based system, that does nothing to the other players. but i meant "good way to strictly limit some sort of hecking in that area" from doing all of the above
4) of course it is possible to change the mac address on your network card (or make it seem that way rather) but better than not doing such a thing i guess >_<
5) therefore the filter would have to be set to only catch 100% spam, not just bursts of whtever over some seconds or whatever :/
my old system was all the opposite of what i've said and i've learnt a hell of a lot and remade it and its a LOT better in all ways really. but meh :/