Turkish and Finnish do have the same word structure and very similar sentence characteristics. Both are agglutinative languages with vowel harmony and "floating" word order. Japanese is also agglutinative but lacks vowel harmony. I'd consider scholars who believe these languages are not similar to be quite wrong.
It's true that there is practically no common vocabulary between the tree though. (Hungarian and Turkish share some small amount of words due to relatively recent Ottoman rule, but that's about it)
An Italian friend learning Turkish complained mainly about having to wait until the end of sentence (The Turkish (and Japanese) sentences are canonically Subject-Object-Verb) to understand what's going on. And imagine a native English speaker's frustration when they realize groups of words can come in any order in Latin (and Turkish, and Finnish) and it's the suffixes that make up a word's function in the sentence!
So, my point was that being exposed to a language with a different grammar is simply good mental exercise and will come in handy when learning other, seemingly separate foreign languages, regardless of the amount of people who speak it.
It's true that there is practically no common vocabulary between the tree though. (Hungarian and Turkish share some small amount of words due to relatively recent Ottoman rule, but that's about it)
An Italian friend learning Turkish complained mainly about having to wait until the end of sentence (The Turkish (and Japanese) sentences are canonically Subject-Object-Verb) to understand what's going on. And imagine a native English speaker's frustration when they realize groups of words can come in any order in Latin (and Turkish, and Finnish) and it's the suffixes that make up a word's function in the sentence!
So, my point was that being exposed to a language with a different grammar is simply good mental exercise and will come in handy when learning other, seemingly separate foreign languages, regardless of the amount of people who speak it.