I think things that cost little or nothing when underutilized are nothing compared to actively wasteful infrastructure. These are all "wasteful now that we have the Internet/cheap computing" examples:

1. Most irrigation systems (efficiency could be increases 3x-10x depending on type of agriculture)

2. Non-smart HVAC systems.

3. Most budgeting systems (viewed as conceptual infrastructure)

4. Paycheck employment models, especially in America with healthcare factored in (viewed as infrastructure for extracting the value of human potential).

5. Democracy. Most constitutions are like IBM mainframes or worse, evaluated as operating systems.

6. Non-agricultural water supply (we flush toilets with expensively cleaned/purified potable water).

7. Sewage/garbage systems (= wasted energy for the most part)

8. Ownership model of material prosperity. Sharing/renting is far more efficient. Most crud is manufactured only to be put in landfills after a few years with hardly any use. It cycles furiously through the global economy (including round tripping of stuff from Asia: new junk one way, toxic waste another way) mainly to enrich rent-seekers who inhabit the banks of the river of consumer junk.

And so on.