Why though? The comic is essentially a straight up spy story, and it's working extremely well. I think they could get away with having Black Widow in an action/espionage type story. The whole point of having a variety of titles is to have a variety of stories. Guardians of the Galaxy is going to be more of a Star Wars type science fiction adventure and I've a feeling that one will turn out OK.
GOTG still has a talking Racoon and sentient tree on a team fighting bad guys. I like the current Black Widow comic (and almost all of her old ones I've read), but a superhero movie needs superhero things. An alien weapon, super bad guy groups with super weapons, just something to make sure its not James Bond with a few Marvel names thrown in. Black Widow shouldn't be killing and seducing random bad guys to get back military defense codes or stop some random terrorists from killing random people. She needs to be stopping some super criminals by infiltrating bases and kicking butt. The character isn't 007, or Bourne.
Its the Marvel Movie Universe. It needs HYDRA, super powered criminals, and/or alien tech in the wrong hands. Those can all fit in a spy story. If people want bland spy stories, they have James Bond for that. BW isn't just a spy, she's a superhero who does things that would kill people like Bond without effort. She can do spy things, but there needs to be things like transforming bears or evil russians in armored suits at some point. Even Captain America has fought bizarre nazi's with deformed heads and his mind controlled ex-friend on a giant flying aircraft carrier. A spy story is fine, but like everything, it needs to have the Marvel style. She can do spy things and fight superhero style threats/plots, and marvel isn't going to do a generic type movie for anyone. They all have superhero/comic book elements, and that's how it should be.