A lawsuit which isn't going to be determined for a very long time isn't going to influence the behaviour of other services now. If it was, then MtGox would already have changed its behaviour as conversion, negligence and breach of contract are all causes of action in the Cartmell et al lawsuit against Bitcoinica.
It's also only going to "serve as a warning to others" at some time in the future if the plaintiffs actually prevail. If they don't, then it's only going to further entrench undesirable behaviour by Bitcoin services.
Probably best to attack them on both the civil and criminal fronts simultaneously. I'm not a fan of regulation, as it borders on prior restraint, though I certainly think we should bring all legal means to bear once the crime or tort has been committed.