Rather than addressing your question with actual names, I'll approach it more from a philosopical POV. I play in a 10-team dynasty with two developmental slots for rookies, which can occupy those spots for two seasons. Historically (speaking only for myself in this particular league), I've had my best success by farming former 2nd-5th round WR talent off the waiver in years 2-4 of their career after the owner who originally drafted them finally gives up. Your mention of Danario Alexander is a perfect example of this.
Obviously, 1st round talent is a whole other discussion (the Crabtree's and Dez Bryant's) of the world. But if you're asking me if I'd rather draft a non-top 3 WR from any given rookie class in dynasty or pick through the WW of former WR's of that ilk, who have been dropped by the fantasy owner that originally drafted them? I've had MUCH more success with the latter.
Regarding non first round NFL talent at WR, my motto has always been, "Be the second team to own him".