I second the Brain - any WCW run-in would have killed the match IMO.
People put too much stock into the lack of stars, or namely that WWE should have held off until they procured their contracts. They like to point out (correctly) that within 18 months of Survivor Series, WWE had brought in Flair, Nash, Hogan, Hall, Perfect, Bischoff, Mysterio, Scott Steiner and Goldberg (and probably more that I've forgotten about) - but who was to know that they would sign? The only one which didn't really make sense was Ric Flair, given he debuted the night after Survivor Series. As someone synonymous with WCW, except for a two year spell in WWE in the early 90s, Flair would have made an ideal and logical leader for WCW, and instantly given them more credibility, so should have been brought in earlier IF they could have done so (I don't know when his Time Warner contract expired). In all honesty, it would have made zero sense, logically, had the original nWo led the charge, since the whole point of the nWo was to 'destroy WCW' in the first place, so why would they come in and try and promote its cause here? Even having Stone Cold made more sense, poorly executed as it was, to further his anti-Vince crusade...
Shawn Stasiak didn't ruin the WCW invasion. I've been watching wrestling avidly since 1990 and was on this site long before I started posting, and before this I used other since defunct sites, and read Powerslam magazine every month etc. and this is the first I've heard of Stasiak's blabber mouth, so that plus the fact he wasn't fired shows that it really wasn't seen as much of a big deal. But imagine the (lack of) credibility had Stasiak done a run-in? His previous WWE ppv appearance was jobbing to Kurt Angle on his debut. Shane and WCW would have looked pathetic. In all honestly Stasiak did the brand a favour.