> This is where you need to use awk.

I think need is a strong statement in this context.

  echo $(( 1 + $(grep 'cpu cores' /proc/cpuinfo | head -1 | awk -F ':' '{print $2}') ))

Choosing shell vs. [insert modern] programming is a matter of trade-off of taste, time, $$$, collective consensus (in a team setting) and so forth.

[edit]: Forgot code syntax on HN.