The permanent upgrades are meant to show how ball speed changes, as well as the goalkeeper speed. We also added a XP multiplier upgrade around the last day of the jam to allow the player to level up faster, especially when the player reaches higher levels that require lots of XP to level up.
Also if you think outside of the box, by making these upgrades permanent, I'm giving the player multiple reasons to keep playing rather than just achieving some high score. This alone will make players want to play this game more and feel rewarded for every upgrade they receive.
You are very right, using Unreal is overkill but I've been loving the engine a lot despite its complexity and how a lot of people working with Unreal run into serious issues with it lol. Not only have been practicing using Unreal in C++ with more regularity, but also I started to understand how to do different things in Unreal as well.
Thank you for your detailed feedback, it means a lot :).