The energy to generate the 2.4GHz signal is already being lost; I don't believe that placing a spintronic device attenuates the signal in any meaningful way. In certain ways it's similar to tidal energy; one small tidal generator is not going to have any measurable effect on an ocean-scale system. The power absorbed is measured in microwatts whereas the power consumption of a consumer router is measured in watts.

It isn't meant for energy delivery, but energy harvesting. Put a metal stick in place of the antenna, the same power is harvested, but dissipated away.

I can see this useful for very low power devices. I don't have specific example in mind, but you can picture something like sensors embedded inside smart concrete high-rise buildings, that alert when crackling is found.