Agreed with everything you list here. I do think it's valuable to learn how to pretty-up and polish the shell prompt. I've set mine up to display the time as well as the exit status of the previous command, along with the usual tidbits of user, host, and cwd.
In terms of languages to learn, the most important is your shell, generally bash for most people. 99% of the time, bash is Fast Enough, even though it can often be very slow. Bash is incredibly ugly, but using its features and the userland tools that are standard on most Unices, you can do a lot of amazing things relatively easily.
For speedy programs, Perl can't be beat. For text manipulation, even C programs sometimes run slower than Perl and generally require more code and are much harder to maintain. Perl is nearly as ugly as Bash and has even more annoyances, but for raw text-processing throughput there's no competition.
In terms of languages to learn, the most important is your shell, generally bash for most people. 99% of the time, bash is Fast Enough, even though it can often be very slow. Bash is incredibly ugly, but using its features and the userland tools that are standard on most Unices, you can do a lot of amazing things relatively easily.
For speedy programs, Perl can't be beat. For text manipulation, even C programs sometimes run slower than Perl and generally require more code and are much harder to maintain. Perl is nearly as ugly as Bash and has even more annoyances, but for raw text-processing throughput there's no competition.