Well poolboyg88, I received a BP from a competition and ended up receiving that same BP while supporting other players shortly after. So unless you'd refuse to support buildings of the same age as the GB you're supporting and winning BPs from... Well, you're always going to risk finding duplicates. So I don't think there's a big difference between receiving duplicate BPs from the "competitions" or via supporting/plundering. Please remember that duplicate BPs will have use later on. We just don't know for what as of yet.
Regards,
Bloodwyn
P.S.: Are you planning on boxing me out of that lighthouse!? :p
EDIT: One other thing I'd like to mention here.
If you wait until the GB that you're supporting has reached lvl 5 or 6, then you might get the chance to receive 2 BPs for second and maybe even third place, maybe even all first 5 places then as well. PLUS the rewards on FP and medals increase just the same... So you'd also benefit from that.
You can always try to get first place as a contributor for the lower lvls, but I'm not so sure it really pays off. I had to spend 35 FP to receive a reward of 20. 25 of those FP I donated, I had to buy in order to keep up with the competition.