in other words, how rewarding it would be

I wonder how do you expect anyone to sensibly answer that?

Any feeling of reward (or lack of it) is a completely subjective thing - that’s like a woman trying to explain to a man how pregnancy or nursing a baby feels or a man to a woman an erection. I.e. good luck with it.

You need to try it yourself and see for yourself whether or not the journey will be rewarding for you or not. Why are you afraid to try? It is not like it costs you anything (beyond time).

not mentioning that elisp is pretty old so the learning resources might not be as much as other more popular programming languages

Did you try to actually look? There are plenty of resources on ELisp and even Youtube videos. While it is not a general purpose language (as Common Lisp or something like Clojure or Racket would be) and it is quite old, indeed (as is Emacs), there is plenty of very good documentation available. I would dare to say even more and better than for some of much more recent and popular languages out there.

like what is the level of mastery do i need to achieve to start implementing custom elisp in my configs to enhance my emacs experience?

Very minimal. Moreover, Lisp is a very minimal language that has almost no syntax that you need to learn compared to something like Javascript, Python or C++.

and how exactly can i improve my emacs experience if i learned elisp?

If you are 100% happy with how your Doom Emacs works, then you don’t need to bother with learning it. However, if you ever wanted to customize Emacs in any way, then you can’t do it without being at least somewhat proficient with ELisp.

And if you don’t want to customize Emacs at all - why are you using it in the first place? There are editors with much better out-of-the-box experience than this old dinosaur. The whole point of using Emacs is that you can completely customize it to your needs - something most other editor can’t reach.