At level 120 it doesn't matter i believe,because the cap is the cap. elite or not at 120 you will hit that cap. it just means when its not elite you will need more V/E to reach that cap.

So to answer your question. 1. Its not necessary 2. There the same at 120.

Elites are generally better due to higher ability.

My personal opinion is that they are worth in the classes: Engis, Fighters and Planesman.
You gotta realize that you need less Vets on an Elite sailor to have the same ability, so at the end what you pay will be the same.

The difference is at the lower levels. Therefore you will get better results with EBVE while grinding to cap.

Engies's OH (overheat) time has no cap, so E/B/V/E are better, but just slightly.
Planesman's air reloading has no cap too, E/B/V/E are again slightly better.
But elites have only +9 in other abilitie's growth, so if you want to have good repair rate and cap SD earlier, you are better with none elites, like:
for engies +12 in engy with +10/11/12 in repair and with +10/11/12 in restore;
for repairers +12 in rep with +10/11/12 in restore;
for planesman +15 in pot with with +10/11/12 in repair and with +10/11/12 in restore;
sonarman will reach cap, no point for elites, thus look at planesman.
all these would make your bb/sub better in rep rate and SD.

I had a boosted elite engy level 66, abd his ability was higher than my level 77 elite unboosted engy.

more than ten levels increase in ability helps a lot when you are still grinding at lower levels. So if you are talking about boosts, then yes, I believe they are worth every cent you pay for them while you are grinding a crew.

As for elites, if you can afford them, then go for them. NF is a game of numbers so a little advantage is still an advantage. But if you cant afford them. +12s are still great!

I have 18 level 120 repairers that are not boosted. And all four of my Soviet reps are unboosted as well.

However for some reason my 120 IJN scout is boosted. Go figure.