I wondered why I hadn't heard of this object earier. I meant to do a web search on it, but I hadn't gotten around to it.
Well, I just did a web search on it. Turns out that I had heard of this object previously. 1991 VG is "rather famous":
http://www.anomalist.com/reports/probe.html
http://www.setv.org/online_mss/1991vg.pdf
And other search hits:
http://google.yahoo.com/bin/query?p=%221991+VG%22&hc=0&hs=0

I didn't recognize it because it's context. 1991 VG is probably not a rock. It's probably a spent booster stage. Of course, as Duncan Steel points out there is the very slight possiblity of it being an alien probe.
I'm pretty certain that it's a spent stage, and of course there is not a scientific purpose to doing a manned mission to a spent rocket stage.
1991 VG can wait until 2016 & it would be worth studying with telescopes to determine what it actually was.
Now, objects in orbits like 1991 VG are out there & would be worth exploring, but I'm back to where I was before- we haven't detected one yet.