I honestly think the guards are not necessary. What I think should be done to make CRZ an amazing addition to the game is that it should be done by level brackets. When you look at the world map it shows what "levels" each zone is. Currently any level range is lumped into every cross-realm zone. Any character from 1-90 can appear. If they took the time to simply make the CRZ lump level appropriate people together it would be absolutely amazing.
Can you imagine attacking someone your level knowing they can't just get a random 90 in the zone to come gank you that's off on the other end camping some other lowbie? It would open up the possibility of having real PvP battles, even in the places like the dark portal. The fights would become a lot more fair (as fair as pvping can get while leveling, at least.) I often enjoy attacking people while leveling, if the fight isn't decided before I engage then it's a lot more interesting, and fun.