Solo mining just increases variance.
Exactly. If you feel lucky, go for it. It could pay off, or it might not.
Aside from any fees, pooled mining just removes (most) variance from the equation.
Solo mining paid off for me with namecoin. I found 8 blocks in 24 hours. I should have found 2 or 3 with my rigs. Strangely enough, all 8 blocks were found by the same card... my weakest card.. a 5830.
Gotta love the pure randomness and gambling aspect of solo mining. That being said, I'm back to pooled BTC mining after the most recent difficulty increase with namecoins.