Facebook is what it is and it may or may not have a long shelf life. What is changing the realm of social media are sites such as Twitter with their instant messages, and so this medium should stay true to itself and not try to copy other, older social media.
Twitter should not change its profiles to resemble Facebook. First, there was nothing wrong with the original Twitter profile format. Secondly, Twitter could come under scrutiny from the company and its followers for trying to copy from someone else. Copying from another company is never a good idea, and Twitte should not do it.
I do not believe Twitter is making a mistake by trying to change its profiles into something that looks like Facebook. Twitter's profile pages have always been far too thin and did not allow members to add much information. I think they would have been better off doing something original, but copying will suffice.
Twitter's new profiles will be helpful because they will be a centralized place where the background of a person is maintained. Often, it can be difficult to tell the background of someone, but with the profile function they can be quickly identified as the actual person or an impostor. As long as the current tweet system is maintained as well it will not be a mistake.
No, Twitter is not making a mistake by trying to change profiles into something that looks like Facebook, because switching to something more like Facebook will make Twitter more user friendly. Limited to a certain number of characters, people cannot express themselves as ably as they can with more options to post photos.