The best way to learn new words

I agree with you ccooley that we don't have to mugup/by heart words as we do for other exams like GRE.
But there are plenty of scenarios where I made mistakes because I do not know a word meaning in RC choices.
Also it affects your reading when you do not have proper vaocabulary.
So I think vocab does affect you internally although not openly.
Can you pen your thoughts regarding this aspect?

Yes - there are a handful of situations where vocab does matter on the GMAT, and this is one of them!

Note that the meanings of technical terms never matter on the GMAT. For instance - if an RC passage is about geology, and a technical term regarding geology is used in the answer choices, that means it'll either be defined in the passage, or you won't need it at all. You can safely ignore all technical jargon, since it's just there to confuse you.

But, they do sometimes use words that many people don't know. For instance, the word 'qualified'. A lot of people think that this only means 'having qualifications', like a qualified surgeon or pilot. However, it also has a second meaning, 'including caveats' - if you give 'qualified praise', you're praising something, but you're also making it clear that whatever you're praising is not 100% perfect. That could cause you to get a GMAT RC question wrong! These situations should be pretty rare, but they might be more common for people whose English skills are weaker. Either way, each time you run into one, make a flashcard and add it to your studies.

I wouldn't recommend going out of your way to find a 'GMAT word list', though. These cases are rare enough that you'd be better off learning them by doing problems.

A great way to do this is just to read a lot, so you get used to seeing new words in context. An kindle makes that even easier, because as you read you can highlight words that you don't know and add them to a vocab list that you can go back and review.

Learning new words is always beneficial if you have time; otherwise, if you already have tons of thing in your mind, and there are still hundreds of exciting stuffs to learn out there, then the only truly efficient way to memorize words is to understand the word from the context or your own experiences