Generally speaking, URL links are "nice to have's" and never "need to have's" in RPGSS submissions. And, speaking as a former judge, if overused or needlessly used, it starts to look more like someone trying to show off their mad messageboard formatting skillz to somehow garner more attention or consideration for Top 32 (i.e., someone trying to show how super-detailed they are)...or, worse, they can potentially come across like they're attempting to educate the judges in case they didn't "get" what the author was attempting to do...i.e., you're basically pointing the judges to an "explanation" for your item's mechanics because you couldn't spare the words to adequately explain it in the item's descriptive text. In my opinion, this is an even more tempting thing to do for the voting public in Round One now, because not everyone evaluating these items is always doing so with the eye or experience of a primary judge...so you feel compelled to include such links in the hopes of convincing people to up-vote you as you educate them on the awesome mechanics your item is utilizing or enhancing.
Bottom line: For me, I almost never considered URL links as a "plus" in someone's favor. Mostly, I just ignored them. And, when you really stop and think about it...do magic items, wondrous or otherwise, get to include URL links in the published books in which they appear? Nope. So, why try to prop up your entry by including them? Someone with Superstar potential should be capable of demonstrating clearly worded designs which enable the reader to grasp their intent, mechanically-speaking, without having to have URL pointers referencing other parts of the book. If you truly need to guide the reader's understanding (which is quite rare), reference the rules it relies upon based on examples of how they're referenced in existing designs appearing in the CRB and elsewhere.
My two cents,
--Neil