If I can offer an alternative to post-rejection angst: just implement it. Do it on nights and weekends, scale down your feature expectations to the bare minimum (for 1.0, anyhow), maybe plan on something that actually has a chance of taking money from paying customers rather than playing the VC game, whatever you need to do.
Its quite viable, particularly for small team sizes, and you will learn quite a bit about business, which will serve you in good stead no matter where your career or further ambitions take you.
You'll also note that there are plenty of imitation-worthy businesses out there which were in your shoes once. Basecamp got written as a side project between consulting work. Balsamiq Mockups was a one-man band. I could bore you to death with stories of niche software firms that do pretty well for themselves.
Its quite viable, particularly for small team sizes, and you will learn quite a bit about business, which will serve you in good stead no matter where your career or further ambitions take you.
You'll also note that there are plenty of imitation-worthy businesses out there which were in your shoes once. Basecamp got written as a side project between consulting work. Balsamiq Mockups was a one-man band. I could bore you to death with stories of niche software firms that do pretty well for themselves.