Wilkinson, plagued by a cruel succession of injuries since securing England's triumph, only returned to the international arena in this year's RBS 6 Nations clash with Scotland.
But Ashton claimed: "I think, as a rounded player, he is probably a better player than he was four years ago.
"He was a hero four years ago because he dropped a goal in extra-time - but by his own admission he wasn't the best player in the tournament.
"I think he's a better player this time and, given the right level of support on and off the field, he'll play a significant part in this World Cup, as can many other players in our squad."
Explaining what he sees as the improvements in Wilkinson, the coach explained: "His game management is better, he's more experienced, he's a little bit more relaxed and he's more knowledgable about the game.
"I know he's not played a lot of rugby since 2003 but he's actually seen a lot of rugby and, from that point of view he's a better player.
"It's a lot easier to sit and chat with him now. He's a lot more mature than when I last worked with him four or five years ago. He's good company, very knowledgable about the game and more relaxed about putting things into operation on the field."
Wilkinson was rated as the best defensive fly-half in the world, and an important attacking force, going into the last tournament and Ashton said: "He's still got all those elements in his armoury, there's no doubt about it.
"He's not played a lot for England since 2003 - seven international games of rugby in four years, which is not a lot by anyone's standards - but he is a more rounded player than he was in 2003."
Ashton claims Wilkinson has lost "nothing at all" as a result of his succession of injuries, but he has taken steps to ease the amount of tackling the workaholic star does in training.
"There's one or two players who might not do as much contact work as others because they more than make up for it when they get out on the field in a game situation. Put it this way, we wouldn't throw him into every tackle in a contact session.
"But he's not dropped any of his standards at all. He's set world-class standards in everything he does," said Ashton who knows that Wilkinson's contribution will depend largely on the pack of forwards he is playing behind.
"As in all rugby teams, it is the guys from numbers one to eight who ultimately determine how a 10 can shape his game.
"If they do the business - and my feeling is that we've probably got players in those positions who can compete with the best in world rugby - it gives 10 that little bit of an easier opportunity to try to shape a game."
Ashton is unconcerned that his own future could be determined by the performance of an England side who have been written off in many quarters after a turbulent four years since their glory days of 2003.
"I don't think you ever shape your own future in a job like this. I think the game shapes your future for you and I would just like to carry on coaching as long as I can stand on two feet - if anyone wants me," he said.
England, whose opening pool match is against the USA in Lens next Saturday, are bidding to become the first nation to successfully defend the trophy, and Ashton maintained: "I don't feel any pressure whatsoever - just massive enjoyment being in charge of a national squad going into a World Cup tournament and a real sense of anticipation and excitement.
"I think the pressure side of it has disappeared now and I hope the players are feeling that and relishing the challenge of doing something which has never been achieved before."
The coach described his feelings as "a combination of excitement, obviously, a massive determination to do well and the added determination to shut up people who have been talking about England around the world for the past three or four weeks."
He added: "I can't believe other people have so much time on their hands to worry about what England are doing.
"If you think I'm a bit fed up of it, you should talk to the players. It's certainly added a little bit of spice to their determination."