Thing is, if they don't plant mines you don't need to buy a sweeper. pios without sweepers are decent enough in a fight to get to vet 2 normally, and especially with flamethrower. I thought the point of the change was to help sweeper engis?
If not that, I really don't see the point in making the change. Without sweepers they vet up fast enough where this is unnecessary, and with sweepers clearing mines is much more simple and less exploitable.
With that change, an unprotected mine will not only result in loss of munitions to you, but also a gain in strength for your opponent (given that successful minesweeping doesn't happen very frequently, the bonus should be significant).
This might completely change the mineplanting metagame. Since there's nothing wrong about the mineplanting game currently, I don't find any good reason to penalise this.
Repairing, on the other hand, happens very regularly (unless tank preservation is potato-level). If the bonuses are too high or too low, we can always adjust them.
Plus, I have no idea if it is even possible to make it so that sweeping awards XP.
The primary purpose of this change is to allow late-comer engineer squads to have a snowball's chance in hell to catch up. That way, if you've somehow lost your vet2 flamer squad, you won't be left too far behind by your enemy (which could be an EFA faction or a WFA faction).