When people remove the overpants he seems, at least to me... less. The serendipity, the mythical innocence of the character fades and he becomes neo and stylised and 'cool'. But I don't think a cool, modern costume is what Superman, as a character, would want to wear, and I don't think it's appropriate for him to do so. I think whenever Superman appears he shouldn't become a 'cool' guy.
I am completely in agreement with this.
Coolness and innocence are in most senses, diametrically opposed. A 'cool' look is one that is sophisticated, clever and full of savvy. An 'innocent' look does not mask vulnerability, and invites trust.
Superman is supposed to be all colors and a handsome face. To dress him up in the functional gear of today's government-sanctioned metahumans or the stylishly fashionable look of post-John Woo action heroes would be yes, practical and shows a sophisticated understanding of what his clothes should allow him to do.
In short, it would be 'cool'. By being 'cool' he becomes less an exemplar of virtue and trust, a man whose battles are merely incidental to upholding that simplicity and open heart. By being 'cool' he becomes a man who is self-reliant, guarded, and dressed to expect danger from any quarter and be prepared for any threat. By being 'cool' he becomes everything Superman is not.
Also... Bass compared the external panties look with that of circus strongmen. He's right. Circus strongmen don't dress to look fashionable or cool. They dress to accentuate their form - regardless of whether it is well chiseled or merely bulky - even if that means looking a tad ridiculous. Why? Because they're emphasizing the BODY that does these great feats, and wearing a cloak and dress pants or a tuxedo would be wrong in that regard.