Could just delete engine trails and alloys from remnants and add them to the gold shop without skull requirement.
It's supposed to be endgame content while it's simular to cake blasters etc. Many don't care and just despawn them to get a 9th item XC. Ez fix for the rotation.
OR .. add some actual buffs for different alloys/engine trails like the insanely expensive alloys from the shop do.
Don't forget that you don't need to spend even a single penny on permanent alloys as well. You can do it completely for free, if you have enough friends that would like to try the game and just invite them to play.
However, in case of alloys from XC Carriers, I could agree that different colours would be greatly welcome to the pool, causing it to be more frequently pursuited instead of just despawned. However, I can't say the same about Engine Trails. As you play on Askone as well, you know many actually would like to put some of those into their ships, i.e. I want to put most of whites and reds to my ships but I am unlucky to get those atm...
Below this, my video about free alloys: