personally i would like people to slowly start transitioning to A grades and not be stuck with C/B grade +++ equipment. i think we are not going to follow official updates from now on and it would be very sad if going for A/S grade would be less worth than staying with C grades +10 and B grades +8, because that feels like game does not really progress
(PS: gratz for 1k posts, welcome to big boiz area :d)
i would for sure not put shop with items like during tiger event, even if prices are ridiculous, if you give someone opportunity to buy bresses cheaper than with CoL or stuff, he will just stack them once again and all this fiesta will never end. let it be full RNG what you open you get, put some very nice rewards but with very low chance as it was said (for example like there was only 2 winners of this green cloak during 1 spring event or something), also i would put less items to be exchanged for reward, but change rewards according to it (so good things will be less likely to get), that way ppl get enjoyment of opening the event items, and eventho they get like 3 buff scrolls, 10 fireworks, 5 qhp, but 1 enchants, it will be better rather than exchanging 3 event items and getting 1 enchant, 1 qhp and 10 fireworks
also you could make interactivity like in tiger/pumpkin/snowman event, where you spawn some creature and have to interact with it (for example there was bonfire event on official), not just exchange at npc and thats it
this daily buff for boost xp was nice (personally it didnt bring as much as i expected coz the numbers were kinda low, would slightly boost them maybe from 3/6/10/15 to like 6/10/15/30 so the last hour would be actually big reward). i would put this buff in the special buff slot like clan unity and other boosts, not normal buffs so it cant be overbuffed. Also if its not big hassle, during this buff duration, you could have special transofrmation on people (i can provide some screenshots from valentine event/halloween event/christmas event from official), that way people feel kinda special and different
tl;dr
1) make event items drop more often (chances to get something good adjusted to it)
2) make less event items needed to open 1 item (chances to get something good adjusted to it)
3) boost a bit last hour of xp buff, making ppl trying to xp more and be out of town on daily basis
4) keep it RNG (except maybe cloaks/aghation how you made it on last event, event items+CoL)
5) let people feel special during event, let them have some fancy transformation and interaction with NPC when trading event items (some might consider it annoying, but its pretty change of pace imo)