He's comparable, to a lesser degree, to Indurain. Indurain frustrated his little climber rivals by shadowing them in the mountains, allowing them to take stage wins, knowing that he would blow them all away in the tt's. Unlike Wiggins though, I believe Indurain could have dropped many of his rivals in the mountains but he was always looking at the bigger picture, that being the overall classification. Chiappucci would go on epic attacks taking time on Indurain only to lose it all plus some once the tt's were over. Wiggins in last year's Tour was never really challenged and rarely had to stick his nose into the wind. The one time that I recall him having to fend for himself, when Froome had one brief moment of mortality and dropped to the back of the elite pack that they were in, Wiggins began to struggle a bit. If any weak links are exposed in the Sky armour, his opponents will have to pounce and to do that they will have to be fully focused and not just sitting in waiting for the final couple of km's of the mountain stages.
I can't give Nibali the edge in the mountains. Maybe on the steeper slopes but overall Wiggins is his superior, much as I would like it not to be so. Nibali though is crafty and relentless. It's this combination of traits that give him a slim chance of bettering Wiggins. Nothing ventured, nothing gained.