But the Narada isn't particularly strong, defensively speaking: mere handguns had nearly destroyed the drill in the previous encounter, and a single small spacecraft destroyed it in this one. Earth must have tens of thousands if not millions of small spacecraft, and Nero's jamming doesn't stop spacecraft from flying or firing. And Nero doesn't have tens of thousands of missiles: the best he can launch ("Fire EVERYTHING!") is about twenty.
After destroying the local starships and possible orbital fortresses, how does Nero survive the other defenses of Vulcan or Earth? It's not the surprise factor, because in both cases, he spends minutes drilling, and Starfleet can respond faster than that. It's not just the jamming, because that doesn't stop small craft or handguns. It's not the shielding, because that (whether raised or not) didn't stop small craft, handguns, or even transporters. It's not the missile coverage, because that's sorely lacking.
It might be information warfare: with defense codes (which Nero tortures out of Pike for attacking Earth, and probably tortured out of somebody else for attacking Vulcan), the local defenses could be silenced relatively effectively. The big guns might be told not to fire, or to fire at each other, while the smaller units might be given confusing orders that prevent them from approaching the Narada while the drilling is proceeding. That's one field in which the civilian miner Nero might get full advantage of the fact that he comes from the future (and has 25 years to acclimatize himself to the present): his ship wouldn't come armed with the latest 24th century military wonders as default, but his computers might still house a few advanced attack programs as default.
As for the Borgifying of Nero's ship, in the comic it happens because Nero becomes the official imperial champion for revenging the lost homeworld - he has time to fly to a secret base and get upgraded. The movie tells us this is flat out impossible, because Nero gets sucked into the timehole created by Spock when saving Romulus. This must happen mere minutes after said creation, before Spock gets back to Vulcan in his superfast ship.
...It could still happen if there was further time travel involved, I guess. And if Spock lied about the sequence of events to Kirk in the mind meld. But mere omission of this further time travel isn't plausible; it has to be a deliberate lie. And it doesn't make much sense, because Spock emphasizes that he was in a hurry and was too late - neither of these are concepts that would apply to a frequent time traveler.
Timo Saloniemi