I would want another type of unit that can be repaired or basically some sort of way to use my droids. I'm almost three years in, closing in on everything being maxed out. I've probably put about $27 into the game, mainly to get additional droids early on.
What will turn me off from the game will be not using the items I paid for. Sure repairing two dekas will keep two occupied, but what will my other three do? Only so much junk to be removed, turret swapping, meh.
1. A third unit to be repaired, deka, support bot, whatever, just something to keep my droids busy.
2. The ability to use more than one droid to repair a deka more quickly.
3. Some type of ability to increase the usefulness of walls. IDK.