So curiously, Cad Bane's ability specifically says to activate him after paying the cost for an upgrade. I presume this means you must spend the resources, and that overwriting an upgrade with another does not count as paying the cost. Therefore, if you overwrite a Holdout Blaster with say LL-30, you would not be able to activate him through his ability, but you would still have the Ambush action?

You can use Cad's ability even when overwriting. Overwriting reduces the cost of the upgrade, and it may reduce that cost to 0, but you still payed the cost.

CBowser is correct. The text in italics on Cad is just a reminder that he doesn't reduce the cost via his own gametext.

Awesome, thanks for clarifying!