I know that avoiding plain toes is the conventional wisdom for men with big feet. I'm a 13D, and I have quite a few shoes with plain toes. Maybe I'm deluding myself, but I don't think they look all that bad or make my feet look extraordinarily large. I mean, my feet are big, but then I'm a big man--they're not that out of proportion. The only shoes I ever tried that magnified the size of my feet so that they looked clownishly large and unattractive was the Allen-Edmonds Seneca. This has a very pointed moc toe and an extended welt. I had thought I would like it because I like the dark brown color, but it just did not look good on my feet. Sometime soon I want to check out the A-E Harrison (a plain-toe blucher) in brown. Maybe it will be unflattering, but I don't think so.
Ah, I think you've hit the nail on the head. Proportionality
is the word of the day, kids. I've seen many a very large man with plain-toe Aldens and AE's that seemed just fine to me, especially in darker colors (as someone above also pointed out). However, if you're 170 lbs and have size 14's US...and especially if they're narrow...then a plain toe or long wing just looks a bit clownish.