Are event crusaders worth getting? I have searched around plenty and have found absolutely NO information on what happens when you get one, so I have been quite uncomfortable with the idea of replacing an old crusader with a new one without knowing the details. I do not know if enchantment points carry over. What are the exact effects of replacing original crusaders with event versions? And if enchantment points do not carry over, the abilities are the same or completely different, and the crusader gear does not carry over to the event crusader's equivalent (common-for-common, rare-for-rare, etc), then what would be the point of replacing a crusader if you lose the old one with all-rare/epic gear?

I think you misunderstand how things work: event crusaders share the same slot with classic crusaders, they do not replace them permanently. This means that you can swap between them as much as you like, the only limitation is that you can't have both at the same time in a formation. The number of crusaders at your disposal effectively INCREASES, I currently have 44 crusaders I can use. So YES, get them. Every single one of them.

Every single event has a 'How to Play' section that details how event crusaders swap with regular crusaders and that the unused crusader sits on the bench. Next time just ask on any of the in-game chats for any question
, anyone would be happy to explain it to you.