I would like to push back on some of the assumptions here:
1. What are the facts around Manhattan people not beting at home most of the time? Where are they? Manhattan people do the same things everyone else does: work, sleep, eat, workout, eat out, entertainment, travel...like everyone else.
2. Many Manhattan apartments are small, cramped, closet less spaces for the simple fact that they are old. I don't know the percentage, but much of NYC apartments were built before WW2, much of it in the 20's or earlier. People did not have family rooms, walk-in closets and sit around in their kitchens. They did on the other hand have high ceilings, fireplaces and beautiful touches, so in the more gracious buildings even studios and 1BRs can be quite nice. I had a 3 BR duplex outside Manhattan years back, with the tiniest kitchen, but a maids room off the back of the kitchen, pretty cool.
3. Not all Manhattan apartments are small.
I think you will not miss the space, but you will miss the storage and some conveniences. Go Manhattan and go small. Consider putting $100 a month towards a storage facility for Rubbermaid tubs of clothing and crap which is not part of your daily, weekly or monthly life. You probably have 400 squre feet of crap that you don't need day to day which you can stack away somewhere in the Bronx and summon a few times a year. Get organized, if you can, you will be impressed at how liberating getting rid of rooms of books, tapes, clothing and crap that you just don't need. You do much better on a 4th or 5th floor walk up; suck it up, you're a runner, and go for the top floor and you will not have to put up with chicks banging their heels walking around above you.