Upload & Sell: On
My lord RAM is expensive on the Mac side. When I built my machine last year (i5 2500K @ 4.4 GHz, 16GB RAM, 128GB SSD, 4.5TB of HDDs), I think I spent $80 for the 16GB of RAM.
The SSD makes a huge difference in general system performance, boot times, loading programs, etc. However, if you have a lot of RAM, you won't be swapping to hard disk during most operations (or any, really) and so you won't see a speedup of OPERATION of Lightroom with an SSD unless you're using it to actually store your photos.
The RAM can do a good deal, but rendering image previews still takes a while, even with a very fast machine with lots of RAM. If you don't want the delay, you can have Lightroom create 1:1 image previews upon import. It'll take a little longer to import, but then when reviewing images, it should be very fast.