Re: Wearing of Hakama at Seminars
If it's an "all styles welcome" seminar and the seminar announcement doesn't explicitly say "hakama for dan grades only" then wear whatever you feel comfortable with.
I wouldn't judge people's abilities by what they wear, but I know that some people do make assumptions. So if you are not sure about your ukemi skills make sure the colour of your belt can be seen.
One thing I really hate that happens a lot at some seminars is that if you wear a hakama you get the chance to practise with a lot of advanced people and if you don't wear a hakama and/or BB you end up practising only with relatively new beginners which can make life difficult if it's a seminar of a different style than what you usually practise. On the other hand if you wear a hakama some first kyus etc (who aren't allowed to wear a hakama) might try to test your abilities...
As other people have said: if in doubt ask!