The main reason I use gvim is for better looking fonts and more colors.
Also, gvim has more potential keybindings available than vim running in a terminal.
Still not convinced. I'll take tmux and a non-gui vim any day of the week.
Agreed, the ability to ^z out of the the editor into the shell to quickly run a command is a killer feature for me. True colors or a slicker ui would be nice but they're not critical to my work.