Personally I found zsh worth switching to even without spending any meaningful amount of time learning to use it. The better tab completion alone is enough to make up for the setup time and the occasional bashisms I try that don't work.
Definitely. Smarter tab completion and smarter word deletion (Ctrl+W) are probably the two "most used" features for me.
FWIW, after ~6 years using Bash, moving to zsh last week was a revelation. I swapped to tmux (after dabbling in screen) the week prior. Has been a good fortnight.
[1] https://github.com/robbyrussell/oh-my-zsh/ is a great source of zsh plug-ins and configs. I use the "simple" theme and the git, brew and gem plugins (amongst others): https://github.com/elithrar/dotfiles/blob/master/zshrc
Bash[1] deletes to the space. Zsh[2] deletes to the slash. I installed Zsh just now to find this out, and I love that Zsh appears to use ctl-w to delete words like vim does.
[1]: GNU bash, version 4.2.37(2)-release (i686-pc-linux-gnu)
[2]: zsh 5.0.0 (i686-pc-linux-gnu)