If I were a developer for a day:
-I would first address the crit/crash/close issue. The majority of problems with Mirrorworld/minigames stems from this.
-I would re-evaluate the original hybrid classes. Some of these combinations are extremely fun to play, however, they have little to no use in instances. An easy way to accomplish this would be to implement sets for these combos(i.e. PATK cloth set or MATK chain and plate). The gear can be bought currently up to level 100 with Ancient Mementos but unfortunately the last set with a bonus comes from Merdhin Tundra. Geared properly a P/W would be a physical force to be reckoned with whereas Wd/D would be exceptionally useful helping to heal a tank while dealing decent mdps. Currently only certain class combos are worth playing. The equipment for these hybrid classes could be available from NPCs at the cost of Arcadia Coins.
-Change the rewards from Siege War to encourage participation. Make participation of Siege War more worthwhile and players will return to it. Perhaps custom honor point stats that cannot be obtained anywhere else but are slightly lower than stats from instances. Maybe randomize multiple Siege War maps to add another level of challenge to each. Each separate map could have custom dynamic elements for players to interact with.
Several of my other ideas were incorporated and released with today's patch. Other ideas have already been covered by other players and I do not want to seem as if I am piggy backing off of them. BTW kudos on the level appropriate crafted equipment. I feel this will help newcomers be able to gear and get to enjoying Arcadia much more quickly.
Garcrist