It's definitely a very small effect. Equatorial launch sites are almost always preferable in terms of the launch itself, and the fact that most launch sites are

It's definitely a very small effect. Equatorial launch sites are almost always preferable in terms of the launch itself, and the fact that most launch sites aren't smack on the equator is due to logistical or political issues. Vaguely related, Baikonur is an interesting example of political issues. It's at 45.6 degrees latitude, but the minimum inclination it can reach is 51.6 degrees, because anything less would involve dropping boosters on China, and China is not enthusiastic about the idea.