Just to add to the discussion: I 100% agree that players shouldn't be doing this purely for the in-game rewards (even because the progression is, as pointed out by someone above, a bit nonsensical, and I take way longer than 30s per sample). I used to do exactly this at Zooniverse long before even having an Eve character, for no reward whatsoever.
However, there are very obvious flaws in the evaluation set, as several players pointed out above. I think it's important that this is brought to the attention of the MMOS crew, because it's a huge flaw in their methodology.
If they're using the evaluation set to gauge how much to trust a given player's guess, they're simply gauging it wrong. Considering that many players must be simply skipping most graphs to grab the prizes, this this becomes problematic. And given that there are lots of these mislabeled samples (I've run into 2-3 a day), they should at least consider adding something for players to let them know which samples are mislabeled, and fix them. Not only for our sake (because it's frustrating), but for their own (besides the obvious benefit of fixing their evaluation set, less frustrated players = more contributors).