I won't write a novel, but using L2ARC for anything is pretty pointless unless you're doing constant reads on multiple large objects at once, and you're consistently transferring them. More memory is always the first thing that will improve performance, partially because it's just faster, but also because the filesystem you're going to be running on (especially ZFS) already does its own caching, which is faster/better.
If this is just a home setup, and not something serving a database or video editing workspace, you won't get any real benefit from dedicating an entire SSD to just caching.