By just sitting on your coins, instead of using them, Bitcoin won't grow! Spend them, and buy back at the same time.
Agreed but it depends on where you are.
I'm in the UK. It's seriously hard work finding anywhere to spend them here. On top of that there aren't any UK exchanges and although Coinbase is here it requires bank wires to the EU which takes days and costs. The instant buying services there are can often have a 10% premium. I spend where I can but it's not practical at the moment.