I've only been on this plane in F. I really liked it, much better than the DC-9 F cabin in my opinion. The seat pitch in F is a little better than the DC-9 and the seats had a pretty good amount of recline. My 22" rollaboard fits nicely in the overhead bins which can't be said for any of the CRJ products.
As far as the OPs statement about having 25% fewer F seats than the older planes, the actual percentage of F seats to Y seats remains about the same so in theory the upgrade chances should be the same.
My elite status is actually on CO but since my upgrade percentage is still at 100% on NW I'll be logging most of my domestic miles on NW this year... Even on the DC-9 I'd rather sit in NW F than CO Y anyday.