Age old question: Big company boredom vs. small company excitement

I imagine that this question has been asked many times in Hacker News and elsewhere but I'll throw it out there again. I'm a software developer for a large (Fortune 25) company working on a mature internal application. Basically I'm coding small fixes and enhancements, researching issues, and generally trying not to break anything. I telecommute, have a ton of autonomy, and have quite a bit of credibility so nobody really questions what I'm doing. Plus I'm well paid.

However I'm basically making no impact on our company, nor am I growing as a developer. I write probably 20 lines of production code every 3 months and spend the rest of the time unit testing and spinning in my chair.

I have a family, a mortgage, and a busy life outside of work so I appreciate the low stress work. But I really miss being challenged and feeling like I'm making a difference in my career. Would the grass be greener at a smaller company where I could write more code, grow as a developer/architect, and feel like I'm making a difference?

Thanks, and please post any links to relevant posts.