Why do they use thermal paste to begin with? Cause copper touching the top of the CPU isn't good enough, heat isn't transferred properly or efficiently enough. Thats the whole purpose of the paste, to make a good secure connection and to move heat away from the CPU as good as possible..
Not strictly-speaking true. In a perfect world 100% flat metal on 100% flat metal is the best way of conducting heat and we'd never need any thermal material. The thermal material is there to fill in the microscopic pits and dents in both the heatsink base and CPU spreader to allow better contact (and get air out of the way).
If you use too much thermal paste it will actually do a worse job at transferring heat.
Nonetheless, I concur with your point - NEVER remove your heatsink if you don't have replacement TIM to hand.