I just installed a Samsung 850 500GB SSD on my 4 year old ADK PC. The PC had 3 Seagate hard drives, 500 GB for the OS & Sonar and 1T's for the Sonar Project files and sample libraries. The mb only had SATA II so I also installed a $45 SATA III card in a PCIe slot. After I had cloned the C: drive to the SSD, all the applications were screaming fast, but Sonar(X3) was still relatively slow to load samples and project files. So I moved my most used sample libraries and the Sonar project files to the SSD. It's really amazing at how fast Sonar is now. The SSD is no doubt the biggest bang for a buck improvement I've ever done on a PC. For perspective, my first PC had a 286 cpu. Bench marking the drives show about 95 mb/s read and write for the hard drives and 495 mb/s for the SSD. If I had to do it over again, I'd buy a 1T SSD. But if you have an older PC, and have a PCIe V2 slot, or already have good SATA III ports, this is an amazing upgrade.

The only knock on using SSDs for audio is that all the writing involved can shorten the life span of the drive. Now using it for simple reading tasks like loading samples & programs makes great sense. I have an SSD as my main system drive and would love a 2nd drive for samples like the Abbey Road kits in Kontakt which take a while to load....just can't afford that luxury right now. the 1TB SSDs are just too expensive....still!
 

I did the same as the op including moving my two most often used sample libraries to my os disc. Then I made a junction link between the original location of those two libraries and the new location. Those libraries load soooo fast now and don't have to "locate" the libraries for old projects.

I moved to SSDs maybe a year ago.  Still can't get over how much of an improvement that has been to my daily experience.
 
I have some pretty full SSDs now and haven't experienced any slow downs.  If it turned out I did experience a slow down based on too many read-writes, which I think could happen after years and years of use, I'd just swap in a new SSD (presumably even larger one).  Presently I have two internal 1 TB SSDs and it's been fantastic.