Re: "carbon and clipless are for posing"
You forgot the
Re: "I need to have my feet available instantly"
I have never had a problem dis-engaging from my clipless set-ups, whether SPD or Look, and whether on my road bike or fix. Riding in NYC traffic, with cabs and peds to deal with, I also need my feet available instantly. If you find yourself *stuck* in your pedals, you are doing something wrong.
Re: "practicality"
I know many people who have a pair of work/office shoes in their office/work place. And the vast majority of these people don't ride a bike to work. They have either sneakers or walking/street shoes they use outside of the workplace and switch when they get to work. It really isn't that hard people. It takes less than a minute to change shoes. And many of these people carry their shoes with them...
Yes, shocking isn't it. And these people don't suffer the insecurities that seem to befall the fix community.
I will concede though, for just bar-hopping and riding around town, using regular shoes is a plus. But, then again, I usually forget I'm wearing my Sidi mountain shoes when I'm off my bike.
Re: power transfer
When comparing a rider using vans and clips/straps with someone using Sidis and SPDs, well no contest whether on the flats or on climbs. When comparing a rider using a proper shoe with clips/straps and someone using Sidis and SPDs then the difference is less so.
Re: clips w/straps vs clipless
The only advantage I see is, as Judah pointed out, the ability to trackstand. Something I am still very poor at. Of course, trackstanding is only useful at stop lights or at the track during a match sprint. So, I've given myself a pass until I spend serious time at the track. Meanwhile, I just do small circles while at stop lights. But, then again, many elite riders use clipless systems on the track and are able to trackstand in a match sprint. So, it may just be technique.
Admittedly, I'm not into doing tricks on the bike: I don't skid, skip, do wheelies, trackstands for show, so there is no added incentive for me to use clips/straps.
But, ultimately, its a preference kind of thing. Some like broccoli, other don't...whatever.