How crap is your computer? I sent some D800 RAW files to someone on here who had a 6 or 7 year old Acer laptop.. forget the processor now, but probably only a Core 2 Duo, with 4gig of RAM and he was able to work with them easily enough. According to him, it was a bit sluggish, but perfectly workable.
Well, I am not sure how are you familiar with computers. The problem is that TIFF file from 36megapixel camera is approx. 216 MB (TIFF CMYK 48bit/pixel) with no layers. If you start to add layers, the sizes increases dramatically.
The 12mb camera produces 72MB. That's three times less. Therefore in order to get the exactly same apparent processing speed, loading speed, batch-processing speed, latency, etc. you need to triple the performance of your computer.
The problem is that CPUs don't have triple as much cores or frequency than they had three years ago. The harddrives/SSD don't have three times more capacity/transfer speeds than three years ago, our home NAS backup storages don't have three times bigger capacity (in fact harddrives are more expensive than they were three years ago thanks to floodings in Thailand) internet speeds are not three times faster, etc. In the best case they achieved something like 20-50% in last three years, while some speeds like I/O remains roughly the same. And you are putting 300% or more load to them...
You might be fine with speed of yout PC, but no matter how fast computer you'll have to sacrifice some performance. At the same time the 36mp resolution is not three times better than 12mp (resolution != megapixels), so we are paying that cost without having all the benefits.
I have 2011 Macbook Pro Core i5, 8GB RAM with SSD (which is still a decent machine even at today's standards) and don't consider the 36mp RAW processing speed as pleasant experience. 24mp is significantly better. Obviously, it depends how exactly you are processing your pictures, if all you do is RAW demosaicing, white-balance tuning, sharpening and producing small JPEG, then you'll might be fine. If you start editing/retouching, planorama/HDR stitching, you will be hit... Thrue, I could built cheaper PC with more horsepower (but not 300% better), but I just don't want.