The border adds some necessary contrast, but in a bad way. It still looks awful without it, considering the black background of the forum, but a relatively small one should be more pleasing to the eye. Overall, it is very well done. You've at least made me into a fan. (Which is amazing considering that I don't usually like sigs in this style.)
In this particular case, a black border would do naught; actually, I'm not really sure if ANY border would work. A 1px gradient border or a 1px one with a color from the 'explosion' could possibly work, although my theory has yet to be tested.
I agree with changing the border to a thinner white. Try a dotted/lined border? idk just experiment and see how it works. I still think the tag is good in depth and flow.
Thanks for the insane amount of replies guys. It really makes me happy to get some excellent critique! Indeed I do. I'll try screwing around with some different border styles and post back here with my results.