trying to adopt an amoral worldview

[Rev. Rye]

Most girls do like nice guys.  They also like confidence and success.  

My own personal take on this is to strive for competence not confidence. There is of course an internal value to feeling confident. However, if there's one thing I've gleaned from the psychological literature its that confidence rarely maps unto reality. It tends to not have predictive value. People report feeling confident about a great many things that they do poorly on; even to the extend of outright delusion. So I've come to the conclusion that confidence has very little utility beyond mental health and attracting a partner. And I'm not entirely convinced it does even that reliably well either. Your display of confidence can be interpreted as arrogance by one person, and cockiness by another, both of which lowers attraction.

Competence in contrast has utility. It is by definition the ability to do things well. And I think striving to do things well creates the kinds of growth than will reliably be seen by others as confidence. And it opens the door to the kinds of successes that will be seen as attractive by others. 

As for the niceness problem. I think the solution is to strive to be a good man not a nice guy.

A good point in general. That said, if I'm reading the OP accurately, since one of his main motivations is being able to get the girl, confidence is certainly key.