Mgreen,
The clusters definitely do not use bulbs. They use SMT LED's. The reason I have my spare cluster is a bunch of LEDs died on my cluster and it annoyed me, so I went out bought a donor cluster and did some soldering work to transplant.
I am about 99% sure the LCD is attached by ribbon cable, I dont remember having to do soldering to remove it. As far as replacing the entire cluster, I'm sure it's possible, but would require programming to get the mileage correct. My experience with getting infiniti dealers to program anything is not very good. I tried to get them to update my bluetooth module, and it took a few trips to get them to understand what I was looking for.
I dont have direct experience with Nissan/Infiniti, but on BMW's, if you plug in a new cluster in the car, the mileage is stored on both the cluster and another module in the car. The car compares the two stored mileages (cluster and module) and goes with whichever is higher. So say your car has 50k mi, and your donor cluster shows 70k mi, the car will display 70k miles. I'm sure infiniti has a similar system in place.
I would think it would be easier to buy a donor cluster and transplant the LCD. While the G25/G37 clusters look the same, if I were you, to be on the safe side. I'd get an actual ex35 cluster to be sure the LCD is compatible.
Here's a cluster that should work for you.
http://www.ebay.com/itm/2011-2012-Infin ... ft&vxp=mtr