If you kill all the harvesters in C&C (and literally all of them), the AI stops producing entirely.
Its very difficult, because they have so much more Tiberium than you. But its possible and fully effective at shutting down the AI entirely.
You need to kill about... 6 or 7 harvesters... to get to that point. (For those who aren't experts at the game, each harvester costs roughly 2x the amount of a typical tank. So killing 6 to 7 harvesters is a really, really big deal).
If even just one harvester gets one collect back successfully, they'll give the AI something like 10,000 credits (vs the 700 credits you get from your own harvesters). So you need to perpetually dedicate yourself to killing literally all harvesters forever more, if you go down this route. Letting even one harvester escape breaks the strategy.
I seem to remember building long strings of walls into the enemy bases - they didn't seem to attack them - and then walling off their refineries. The harvesters would just stop.
I don't think they AI's spending was linked to it particularly directly though. Felt more like a simple counter "build 1 tank per minute" type deal