I have a sandforce 550 mb/s solid state drive which I run my OS, elite dangerous, and other games from. It definitely helps in a lot of ways. I'm able to load my caches information very quickly (pagefile), loading times are low, and if there is a new texture it needs to access from the SSD for a game, it does so with minimal impact as the seek time is near instant. It is very rare that I encounter performance issues with my rig.
That being said, I also have an 8 core processor running at 4.0 GHZ, and a nvidia GTX 860.
For your question about breathing life into aging hardware, it entirely depends on the problem you are having. If it's taking a long time to load information into memory, but the memory is able to perform the calculations fast enough once it's there, then yes, a solid state drive will definitely help you out. In any situation where a game is loading data, it will be faster, assuming your memory can load it quick enough (It really should unless we're talking ddr1 or maybe earlier)
For elite dangerous, if I launch the game, I'm good to fly in about 40 seconds. From hitting play, to the time I'm in my ship ready to launch or play/whatever, it takes me exactly 40 seconds.
Important notes:
- If you have constant low frame rates, not just pauses while it loads information, a SSD will not help you.
- If the above is true in any fashion, or just on high graphic settings, it will not improve performance.