If you nullify the effect of speed potions during woe, you would have killed the speed potion market which is a lucrative one specially for new players. We've already made a mistake of killing the EDP market, don't want to make the same mistake twice.
I agree on boosting up the guardians too. Players just run past them with no trouble at all. I think making attack speed very high makes it kind of unbalanced since it would in a way paralyze a certain player. Maybe 193 attack speed plus quagmire as a skill and can be cast at a specific interval of time.
Maybe it would be a nice idea to make Us-Euro castles at 2-2 apiece. My reason, US woe has too many castles. There are currently 5 active medium-big guilds: Loli Kingdom, Transcesion, Predicament, Extinction, and Empyrean. Trans and Pred stay and defend at Alde and Payon respectively, the only "challenge" they have, is when the castle's eco is not yet 0, so Loli keeps attacking them. But basically they keep the same castle every woe coz Loli Ext and Emp goes to Pront. If one castle would be transferred to Euro, this would encourage PVP and just not rushing the emp. Sanc and Safety wall has already been boosted, if the breakers don't kill the defense and the safety wallers and sancers first, then it would take a hefty amount of time to break the castle. This would also minimize the number of people going solo since there are only 2 castles left, which means there would be far more competition and people hitting them than if there are 3 castles.