ACK!!

So, I had a new dream-inspired tale pop into my head and I think the concept could really be a winner.  But there are some problems -- one of them pretty major.  I'm not ready to go from writing this:

to this:

That's right.  My idea (which I couldn't stop contemplating on the way to work and finally had to write out a synopsis for), is middle grade.  I don't write middle grade.  I certainly don't read middle grade.  ACK!!  There's not even romance in middle grade.  And yet this idea could only appeal to a middle grade audience.

So what do I do?  Just walk away?  Leave it on the back burner until maybe the right time comes along?  I just don't know...

What do you do when inspiration strikes for something that's totally outside of your comfort zone?