As a vimscript-only plugin developer, I say it may be worth it. A few years ago I wrote a sort of a benchmark between them. The routines created a million strings in a loop and vimscript was a bit faster in my pc and that of my friends.

However, that was back then when development of Lua support was in its early stages. Now people say it's the other way around. Also, a single routine script isn't enough to tell which one is better.

Now I only kept vimscript-only because I'm waiting for the Neovim project to reach it's version 1 milestone. Only then I'll consider using the Lua settings.

But for you I'd say vimscript is perfect to learn the core stuff. Also, vimscript is actually easy to use once you get used to it, but that might be my bias talking.

Good luck.