If shell scripting fills all your needs, then that's a good thing.
Sometimes you might find you need to do something a little more complicated than bash will do for you. If that's the case, consider
Perl. Choosing Perl as the next step has one advantage for your employer: If you get hit by a truck, many of your potential successors already know Perl, so your employer's investment in any Perl scripts you write will be preserved.
My son the network administrator, on the other hand, uses ruby as his beyond-bash scripting language of choice, all my lectures to the contrary notwithstanding.
Young whipper-snapper.
grumble grumble