I was able to enable Vcc and Gnd by tweaking the associated package file:
By default we see the pin definitions for each IC or integrated circuit under the /share/simulide/data/ic74 directory:
bash-4.3$ ls -1 | grep package | sort
If you look inside a package file, for example 74HC139.package, or any other package you will see lines
indicating the Vcc/Gnd are tagged as unused. If you modify those lines to reflect type="" instead of type="unused"
and save them, then you will be able to connect Vcc lines on associated IC to associated Voltage source
Same applies to ground connector as well. I think it helps aid understanding of circuit for students to see the visual
connections to Voltage source and ground. I have made those changes to my installation, and have not noticed any issues with simulation. All appears to work correctly with various circuits.