From what it looks like, this is a horrendous balance change the way it is. I will accept the base builders crying, vocally, and that pushing a change. But twelve grenades for a single wall is beyond stupid. The "balance" really feels like it only takes into account people that put a single wall in a shed and call it a day, this would be fine. However, when you come across a base that fills an entire appartment block, even with 5 grenades to destroy, it would require tens of grenades, a figure probally around 50-60. Your changes does not account scaling, at all. If you have to say I need 40 grenades+plastic to get into a base, thats over the top.
6-7 grenades would seem fine and keep them happy, but the plastic needs to break wood, when the CLE kicks in it will be rare enough.