Does RAM Disk Improve OS X Performance?

Yes - anything you do to reduce the number of writes to an SSD will prolong "the life of the drive". Also yes - the memory (RAM disk) is an order of magnitude faster (between 10 to 1000 times as fast based on what exact workload you want to measure) than just the SSD.

Whether you ever get to a point where your SSD fails due to write exhaustion or if something else breaks first (or you sell the device) is hard to estimate even for a statistical group of 1000 machines used in a proscribed manner.

I wouldn't worry about trying to extend my SSD life and instead worry about making the Mac you have work well for the specific tasks you need. The OS already caches much of the filesystem to RAM, so you'll need a very specific workload to do a better job at caching than the OS already does for free. Also, a repair part is not that expensive should you actually wear out that one part before you're done with that computer. Yes, try not to have un-necessary writes and thrashing an SSD, but since Apple designs the SSD to be covered under AppleCare for three years - it's not in their interest to have lots of SSD needing replacement due to them picking a part that won't last long enough in practice.