My thoughts on the Asgard is that they were relatively young as a species when the Ancients were old. So while the Asgard techologies are very advanced, they aren't at the Ancients level. Seems like they have been quite a bit more worried about trying to add reproduction or new genetic materials back into their species than anything else. Technology comes in many forms and not all of it is meant for warfare.
I think only the Replicators really forced the Asgard to improve their ships and weapons. Thor's ship wasn't able to penetrate the shields on Anubis' ships but surely the O'Neil class could.
