[Snowflakian]

Avengers kind of proved costumes need to be updated tbh.

Cap - Iconic, but even his movie commented on the costume and gave a reason.
Ironman - The suit is Ironman. So it has to make sense within technology
Thor - not really a costume, it's his homeworld's style. It's just what royalty and his race wears.
Black Widow - Shield issue outfit, but also just a one piece suit with a belt anyway.
Hawkeye - His "costume" is another shield issue ops suit and he has sunglasses. The comics changed to match him because his comic costume was "classic camp."
Hulk - It's Hulk. There is no costume. Big ass jolly green giant is hulk.

Falcon is unknown still.

So Wolverine not having his costume makes sense. There's no purpose behind it.
The X-Men costume changes make sense too. They started out with yellows and blacks, those then evolved to straight up black fake leather ops suits over the course of 40 someodd years with the movie timeline.

Other movies:

Kickass - It's all about the rhetoric with the costume. The absurdity is the entire point. What made the movie in the end not work(though still enjoyable!!!) were the rampant script changes that destroyed the heart of the story and the reality behind it.

Dredd - While keeping the helmet on for the film, they still updated the costume to make sense.

Batman - The Psychology and other points of distraction from where the main body is and hiding gadgets too among more.

Man of Steel - Unknown without seeing the movie.

On costumes it's not about that it can't be done. It's about what are the reasons behind the usage and does it make sense for this property. Some do, some don't. Some you can't do without the costumes as it's an integral part, other's you can't do with the costumes because it just won't work. There are some that can be panel to frame, and there are some that's not even remotely possible. It's a balancing game based on a per what each property needs type model. There is no single one solid way to do comic movies.

I see the reason on skipping the Wolverine more towards because there is nothing worthwhile that can be done from this movie that hasn't already been done or proven to not sell. Yakuza would be MiB all over again, and Ninjas are already all over the place in other lines.

We might see something closer to days of future past. That seems like the best place to do X-men past present and future for movies and comics. Even without that, there's still New Mutants down the line, and the last X-men prequel film.

So skipping a few FoX-Men flicks to alternate later seems smart. Let people burnout on Thor, Cap, IM and Avengers, then switch it up to X-Men again later.

Plus there's also the fact Fox may have a different licensing cost as opposed to things Marvel done.
We've seen it with Sony too. Megabloks having the spidey film rights, but lego having the comic and ultimate spider-man toon rights.