Suggestions: See above 2 posts for my feelings on strict 50/50.
Spells:
Its hard to say anything but "scrap it all" or very large changes. When I saw the spells, I instantly forbade the use of 20+ points. These spells are only useful when they are free, since most cheaper spells will bring the same end result (the spelled person's lost). The cheapest spells are the strongest, uncoincidentally. Sectum not being 10 points creates a spell that gives a good chance of being free points. Using Obliviates whenever you can is desired, as for 5 points you take as little as 20 from someone. 15 points, at least. Confundus and the other mark changers (but especially confundus), are wreckers in a strict 50/50 environment (less so if the restriction was lessened). Deletrius is only useful when the high cost spells are used, IE when they're free. Defense spells should cost less, as it doesn't seem right that you're more punished for using the spell than they are for having it blocked (15 points is a lot compared to the other spell costs). Engorgio is alright. Strong. Legilimens should have a price increase but be able to used the round before to learn of the target's deck before the deckbuilding round ends. Otherwise you need a 2 spell combo to use it.
Punishments need to be more followed. There were instances of completely disregarding the deck building punishments.
For the events: Possibly if a team was to repeat an element (Ravenclaw with air, Gryff with Entropy, Slyth with water), they get the element they otherwise would have missed (light, in this case). Makes it more interesting, at least. Or possibly these 4 days would be randomized for each team so we aren't fighting the same element as we're building with. Half Blood Prince is alright, Deathly Hallows is alright if a team is limited to 1-2 avada's being cast against them.
Which brings me to my next point of the spell system letting 3 teams gang up on the leading. Definitely need to change that, possibly with a limit to how many spells can affect a house on a given day/the whole week.
Would prefer a Bo5 in most cases, but with how this event felt like it was dragging on from the delayed start to the large break in the middle, I'm glad there was only 3 matches for each time I had to play.
Some more may come later.