How honest should I be in disclosing not-so-exciting results?
In research, you don't set out to prove that something is true. You set out to discover whether or not it is true. This would be knowledge. The other is just propaganda. 

Negative results are not a failure. They give you evidence just as do positive results. If you ignore, or obscure, results you are lying to yourself and others. If you design an "experiment" so that it is guaranteed a priori to produce positive results, it isn't research. 

Hoping that something is true isn't evidence. Many researchers start out with that idea. I think this is true. I really want it to be true. But if it is false, it is just as valuable (possibly more so) to know that and to be able to investigate why. 

Report all your results. Try to explain why different aspects lead you in different directions. Only then can your learning begin.