I must say that upgrading memory does not improve performance, it just let you open more tabs, that's it. With 2Gb of RAM, you can mainly have 5-6 tabs open before getting a slowdown, it does not actually speed up things.
As for the SSD drive, it does cut the boot/shutdown process by half, but that's it. You won't gain anything else than this, You won't get a faster opening in tabs or whatever.
All in all, I won't actually recommend getting a SSD for this, not a big one, if you manage to get a small SSD for 40$, ok, but other than that, it's a waster of space and money. If you do, get one 7mm thick, otherwise, it won't fit in.
As for memory, if you're only using 5-6 tabs in your chromebook, keep it that way, you won't notice an improvement either.
Maybe those 2 upgrades will make a difference in the future when Chrome OS will get updates, but for now, is pretty much useless, wait for the updates in Chromes OS and then buy RAM and SSD if needed, prices will be lower.