Part of what hasn't been mentioned yet in favor of co-founders is that on the right team everyone makes everyone else better. Or, in this case, with the right combo you both make the product better together - over time. When I see someone focusing on the immediate benefits of a co-founder, I wonder if it's short sighted.

For an analogy that may resonate with this community - think about a hacker house or group of programmers that are friends. Those relationships can make each of you better programmers. In effect, you're each helping each other move from, say C or B players, to A players. Imagine if you only thought someone at an equal or higher level than you could teach or help you with something.

You might carry more weight for the first 2 years, your partner's skills may become more valuable for the 2 after that. That's either a reality you accept in creating a true team or a point of tension for you - depending on your personality.

Of course, a solo founder can be a part of a community that helps them become better, just another perspective.