MOAB-SHREDR upgrade (2-3) does extra damage to MOAB class balloons. The MOAB-SHREDR upgrade costs ~$3k (after 2-2). The final upgrade to 2-4 doesn't change anything, except giving a special ability (is that correct?)
The spiked mines path (4-2) costs much more, ~$15k past 2-2. They quickly pump out spiked balls that have a final explosion when the spikes run out. They seem much more destructive, but don't have that "extra damage to MOAB class balloons".
My question is, which path does more damage to MOAB class balloons? Could the MOAB-SHREDR upgrade be worth more in damage than the other path, despite being $13k cheaper?