I measured the current consumption of the 8042 MCU by inserting a milliamp meter in the +5V supply to the chip. It confirms reports of other experimenters that it's scandalously high compared to modern MCUs. I measured around 80 mA. I only sampled a few chips—no time to test every one—but there was little variation across the NMOS chips by age or manufacturer, or whether it was a ROM or EPROM part. However a couple of chips labelled 80C42 made by NEC only drew about 8 mA, far better. Whether NMOS or CMOS has a greater impact on the current draw.

You won't feel the difference by touch; 80 mA means 400 mW dissipation, barely noticeable.

So, generally not a MCU you want to use when power is limited. But you should look at the whole application. If you are driving heavy power devices then the amount taken by the MCU may be insignificant.