I'd guess that increasing pin count will probably tend to increase energy efficiency, all else held equal.

You need to pull the voltage up and down more quickly to run at a higher frequency clock if you want to move a comparable amount of data over a small number of channels than over many parallel channels.

That means more loss of electrical energy to heat from capacitive reactance.

The more you can do in parallel at a slower frequency, the less you run into problems there.

You're joking of course but that is the direction it's going

I'm guessing, however, that soon we'll start going towards 3D. Current CPUs already have multiple layers but that still causes issues with cooling. Once that gets fixed, I see us ending up with cube CPU's that generate shitloads of heat