I am actually working on something similar-ish, but since I am in stealth mode I won't say what the differences are, and I am definitely aware that it is a difficult area to get into. You need a recognizable brand and a certain starting size to get it snowballing.
I have the luxury of doing it for my own personal enjoyment, so I don't have any concerns :)
I struggled with bouncing from ideas too long, and really there isn't one factor that makes or breaks an idea. A lot rides on the execution. So start executing to start making some new mistakes to learn from, thats what I am doing :)
Try maybe Prosper? Or ask your friend engineers? The money at YC's levels can be found just about anywhere. The YC 'bump' with expertise, connections, etc, is likely of very high value, but zillions of people get by without it.
It sounds like your ideas may not align with YC-- maybe it's them and not you?
If you've proposed 5 times, you've got more gumption than a lot of entrepreneurs-- just keep moving.