More RAM lets you use multiprocessing better, which lets your computer render more frames at the same time. While the render will be faster, however, starting the multiprocessing render or RAM preview in the first place takes longer than starting a non-MP render or RAM preview.
More RAM also allows Ae to cache more frames in RAM when you're not using MP.
The SSD will let you cache more rendered frames, meaning you'll spend less time re-rendering frames you had rendered once but which had to be removed from the RAM cache.
Shorter version: more RAM helps you render frames faster the first time around, if you are willing to wait for the MP startup. An SSD helps you avoid re-rendering the same frames more than once.