The Klingon sequences were cut from the movie, IMHO I suspect because it would have created more questions that it would have answered, i.e. even if the Klingons couldn't completely understand the tech, they'd have torn the Narada apart in the twenty years they had it in their possession searching for answers.
had a hard time dealing with the missiles, George Kirk was able to keep the missiles off the escaping shuttles, but not able to protect the ship at the same time. Enterprise
appeared capable of holding her own during the second encounter, but was still overwhelmed at Vulcan, perhaps the fact that they were protecting the jelllyfish at a distance rather than targeting missiles directed at her made the difference? Or, it could simply be that by then they knew exactly what they were facing.
As to the Narada's limited missile load-out, perhaps it was simply intended as purely defensive? Try to take this ship, and we WILL
But, as you pointed out, she seemed to have had limited ammunition. This would fit into the theory that she was designed to defend herself, not take part in long-term military actions.
After destroying a Klingon fleet, taking apart the Feds at Vulcan, and pounding the Enterprise
, Nero simply didn't have the time to replicate restocks, using his last available salvo to try to take down Spock.