The problem with scaling to larger numbers of transactions is that block sizes become bigger and it takes more disk space and bandwidth to run a node. But, the bigger we make them, the more transaction fees there are, so incentives for miners would actually go up.
(very marginally so - block rewards are like 100x as high as the transaction fees, which actually leads some miners to not include transactions at all - trading off a 1% lower payout for faster propagation times and an increased chance of "winning" if they successfully mine a block at nearly the same time as another miner)
On the large scale, I don't see mining efficiency affecting total bitcoin power usage, but I do see rewards impacting it. (higher BTC price => higher economic incentive to mine => more investments in mining operations => more power usage)
I think a lower bitcoin Hashrate would actually be a good thing (for power consumption and pollution)