I was calculating how much cost to make warrior shell +7.
So here it goes:
1. I can make in average 1 of 5 shells from +1 to +7, which is good statistic.
2. For upgrade i use NUSx1 + BUSx5 and that cost 264k + 5 x 2.64m =13.5m
3. Shell +1 cost 1.5mil - 2mil
(13.5m + 1.5m) x 5 = 75m
Of course, not every shell burn from 6->7, so u save there 10-12m per tour (some got burned on lower +).
So at the end u get shell for 65m.
And dies is full of shells +7 that cost 50-55m.
CONCLUSION: Upgrade of warrior shells on dies doesn't pay out.