Re: who can wear hakama
In our dojo the hakama are for Dan grades only. I think it's a good and a bad idea, on both counts because it gives you something to aim for. And as many others will point out, there's something humbling about tripping over your hakama (one sensei at our dojo refers to it as the 'Hakama Technique').
However, it's also just a piece of cloth; traditional Japanese clothing that's been around for much longer than Aikido has. To that end (combined with all of the early 'tradition' of it being what your average aikidoka wore), I do find myself wishing that we were all encouraged to wear one. If for nothing else then to appear as aikidoka -- silly reason though that is, I find the hakama satisfyingly adequate at defining a generic martial artist as a practitioner of Aikido.
I think that the best approach is to just keep in line with whatever they say where you train (whether permanently or just on a passing visit), and have the hakama mean to you whatever it does outside of the dojo, if anything. And be prepared to don or or remove one in-line with the wishes of whoever is teaching, regardless of your rank.