Well put.I consider a 3rd rounder a fairly high investment (for most positions). A QB or LT, (and maybe a couple others) are exceptions to this. Yeah, like 1st round picks, nobody is a "sure thing" and there are busts. But overall a 3rd round pick may need a BIT of work to shine, but he should be a solid starter at some point.
Now, a 4th round or later pick is more of a crap shoot. And a 7th rounder is about on par with a UFA in my mind. About as many UFA's seem to stick on rosters as 7th rounders.