Does the fact that it's worked for all of those years mean anything?
What about the fact that this look is "classic" and instantly recognizable?
So, your basic argument is "if it isn't broken, don't change it," right? I guess for me, I look at the classic version and I feel like it IS broken, or at least very dated. Certainly, that is just my opinion and not fact, but the underwear-out look just doesn't look like something that would appeal to a modern audience to me and seems to be a relic from a bygone era, just like bellbottoms and zoot suits. Now, if the movie was a period piece, sure, why not, but I am assuming it will be set in modern day, not in the 30s.
Or the fact that the 'red undies' (and c'mon.. calling them "manties" is just silly and demeaning - you're trying to poke fun to help make your argument) break up the costume and make more design sense than unitard look? The aesthetic is just poor in my opinion (but, then again we could just add every texture and kiddie-Photoshop trick to the logo for the sake of modernizing - sorry

).
The "manties" thing isn't demeaning. That term started (for me) getting tossed around when we bought the costumes from 300, which included leather manties. It certainly isn't shoring up my argument.
Yes, they do break up the costume design, but the question is whether or not the design needs to be broken up. I suppose that simply comes down to another opinion, but the issue I see is that again the underwear on the outside immediately dates the costume and if the goal is to break up the suit, I am sure there is another way that could achieve that goal without making the costume look so old.
In regard to a unitard look being a poor aesthetic choice, what makes you think that is a poor choice? I would say for someone who flies, the more aerodynamic the better (which could also make for a good argument against the texturing used on the new suit).
Stuck in the past!? Dude... that costume has been around longer than any of us. To say it/we're stuck in the past because they're changing a character design just to "modernize" or change for change sake is just writing off history. It's forgetting what works and has worked. You can make changes that do work and retain the history and the elements that are successful (see John Byrne) - I don't think they're even trying with the new Superman look... it's just poor IMO.
We just aren't going to agree here, but I think this goes far beyond Superman and touches on a difference of core beliefs that you and I both have and already know that we don't see eye to eye on. I am, typically, all for change and modernization and not feeling the need to stick to dogma. You are not. Neither of us are necessarily wrong, it is just a difference in outlook. For me, most of the amazing things we have today is because someone decided to break the mold, throw away the past and try something different. Many times this fails, but when it succeeds, we take a giant step forward. If we always looked to the past and said, "this works fairly well and has worked fairly well for a long time, so why change it?" we wouldn't have much of the modern things we have today. I see the Superman suit the same way. It has been the same for 70 years... but the world is not the same as it was 70 years ago. In fact, the world today barely resembles the world of 70 years ago at all. People and human nature is more or less the same and always will be, but the world around us is drastically different, so why wouldn't Superman's outside appearance change to match that, unless you were doing a "man out of time" kind of thing like is done with Captain America, and even he got a costume update!
...and once we accept that Superman is a classic character recognzied instantly by millions if not billions and changing his look merely for ego (hi, Jim Lee) or just for allegedly modernizing him is just silly.
See my above comments. I couldn't disagree more. Now, I can't argue about the motivations of this or that person for making changes, but not every change is motivated by ego.
You can't realistically claim that taking away his shorts, darkening his color and adding a texture isn't following a trend or a fad in today's comic book movie world rather than just letting Superman be Superman.
Let the icon win. Be above trends and fads.
I can see the merit of this argument from a certain POV, but at the same time, I still think you are relegating Superman to a past that is barely relevant in modern day society. Do trends and fads change? Of course they do. Why wouldn't Superman or any superhero keep up with them on some level? Let me ask, do you think the modern Batman movies would have done better and more iconic if Batman were wearing the Adam West costume? Do you think a modern audience would take him seriously? They definitely modernized his costume, even from the already modernized costume of 1989, yet no one seems to be confused about who Batman is and those movies don't seem to have suffered financially due to the changes. So, what is the downside?