TBH, the only way you'll really notice the trait thing is if you know the basic traits in advance, or have another officer of the same race you can compare with (well, one that has thoswe traits as well anyway). And with the lower ranked BOs, you might be less likely to see the rare skills...
From what I been hearing if you get one you might be better off training the best skill to an existing BO already assigned because when you recruit the new BO into your crew for some reason the skills change and you end up not getting what you thought you were gonna get.
Rare bridge officers can also have cosmetic differences. For example, you can (currently) only recruit female trill science officers. I was rewarded with a blue Trill science officer who had some improved skills, but more importantly was male, which is not currently available for recruitment.
Also, when I hit admiral in OB, I was awarded a "very rare" (purple) trill tactical officer, which was female, and currently only male Tac officers can be recruited. I had made a female alien tac officer to customize to look like a trill when I was a LT. as I couldn't recruit one, but apparently they are rewardable as very rare items.