edit: Waste might even be exponentially proportional to bitcoin value...?
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)