I am a big fan of vim myself. I also think if you are working efficiently in your editor you should stick with that. If you are just hoping to improve your skills a little for when you need it there's a pile of tutorials out there that will give you a little better grasp of vim and maybe make you respect it more.
I use rails.vim plugin for my projects and it does a lot of textmate type actions for you.
Might want to try that out if you have not seen it. Make a folder .vim/ in your home directory and unzip the file inside there. There are some other great vim plugins out there. snippetsEmu is another that you can find on vim.org that will give you a bunch of predefined snippets for languages which you are probably a big user of coming from textmate.
Oh Last thing, tpope the author of rails.vim has a nice little video on his page showing off rails.vim if you want to see what it's all about.
Hope that helps a little.
I guess if the only question is what makes vim useful is how easily it can be extended to do what you want. When I started to learn rails I drooled over textmate myself and I been a long time vim user. The great thing about vim is if you start looking at plugins you can mimic textmate pretty easily. That is what makes it useful in my eyes.