I think your relationship outside of sex is hugely important and I agree with everything written here. And when you do all of the above, it has to be genuinely to improve your relationship, and your communication, not with the sole aim of getting in to bed.
But also, in a long term relationship, the quality of the sex has to be good too and what constitutes "good" for women is sometimes not the same for men. I am not saying that this is the case necessarily in your situation op but it's worth considering.
One of my ex bf's thought he was an excellent in the bedroom because he had a lot of stamina, and without going in to a lot of detail, he thought he knew what I liked but he didn't really ask and he guessed wrong. It wasn't that he didn't put effort in, but he didn't put effort in in the right way and didn't really listen.
And ultimately, if you have sex over and over and don't get pleasure from it, and you have hinted, guided, tried to explain, and they don't understand or try to listen, you don't want to do it anymore.
Also, some women have problems explaining what they want and fake orgasm which also is ultimately disastrous for your sex life because it results in the scenario above. Many younger women, or unconfident women, have this problem.
Final suggestion: is your wife stressed about anything? Is she feeling depressed for any reason? Does she have time to herself to look after herself and exercise? Does she feel confident in herself? Sexual attraction can be as much about how you feel in yourself, as it is about how you view the other person. Is she feeling down and unconfident?