I don't dress for men. Maybe my being queer has something to do with that, but 'Do I look sexually attractive in this?" is not why I care about fashion. Sure, it's a part of it -- it's a part of everyone's daily routine -- but it's never the sole motivation.
What I like about fashion is that ultimately, in theory, it's the only sort of 'art' that most people care about and incorporate into their daily identity as a way of expressing themself and their ideals, even if they aren't entirely aware of it. I feel sorry for heterosexual men performing as masculine in a typical way because society doesn't let this be so much of an option for them -- and for girls whose main concern is looking 'sexy' when they dress themselves. The people who I admire and who I like to associate with are often the ones for whom more motivation and thought goes into how they project/express themselves through their style.
When I was 15 and dying my hair blue and dressing in all black to distance myself from the cheerleaders who mocked me or whatever dramatic teenage scenario we want to talk about, what was I doing? Trying visually to express that what I felt/thought was different from them, and that the people I was attracted to do the same. I'd like to think I'm more grown up now, but essentially I'm still doing the same thing.
If projecting sex appeal is what you want to express -- and certainly for most people it is -- then that's genuinely awesome -- but then again, a huge part of that is what's 'sexy' and to whom are you trying to 'appeal'? For a painfully obvious example, don't you think 'butch' lesbians are putting a conscious effort into looking that way, which is probably NOT what the OP's male friend thinks is 'cute and sexy'? But clearly it's not 'pointless.' Projecting a certain sort of sex appeal is a part of everyone's identity and fashion inevitably factors in.
My boyfriend loves when I'm more 'fashion'y / exposing less / maybe even being a bit androgynous, and if I want to 'look sexy' for him, cleavage is not the way to go. If anything I try to make myself a little un-typically-sexy, because I think it sends more of a visual message about the sorts of people I want to associate with -- and the sorts of people I'd want to sexually appeal to as well.