I love this! I think it has great potential to be its own song, or an intro/outro to another song, or possibly a bridge. I actually like the vocals basically how they are with the instrumental, to be honest.
What I do, is I have a folder on my computer that I just throw into every miscellaneous idea that I get, and save for later. Eventually, I'll have enough pieces to put together to make a song, or have that one final piece that I need to put with a song that's almost complete.
I also like to let ideas ferment for a while, so if you aren't sure what to do with this idea now, it might find a place later in a song for you. Whatever you do, don't throw it away! I've had ideas I've saved for years that I thought were a little lame, but I'm glad I saved because they ended up fitting perfectly into a song, with some fleshing out.