This is probably not the reply you're looking for, but here goes. Why don't you ask your wife how she would feel if you only made $10,000 a year or you only spent time with her 2 evenings a month or you weighed 350 lbs. and you refused to try to improve the situation. I think it's okay to tell her that unenthusiastic sex once a week is not only below the level you're willing to settle for, it's below the level any "normal" guy would be willing to settle for. Feel free to ignore me, but I just read an article on the way postmodern beliefs (everything is relative) are destroying our ability to think rationally. A little common sense is all that is needed to figure out exactly how cr*ppy your sex life is, in the same way that it's pretty easy to figure out whether you are more overweight than average or that you make less money than average.
I would say the average woman based on discussions with peers and a lifetime of reading women's magazines and fiction has the following point of view about sex. She wants sex at least once or twice a week, likes getting head and is a bit ambivalent about giving head, most positions are fine as long as they're comfortable, dislikes doing anything that she thinks makes her look unattractive, likes some romance with her sex, orgasms fairly easily with clitoral stimulation, is 50% likely to be not into anal sex, quite possibly wants more foreplay, dislikes or is bored by porn, likes sexy underwear but is ambivalent about costumes, has faked an orgasm on at least one occasion, is more or less horny depending on the phase of her menstrual cycle, likes a cute male ass, has "light" domination fantasies, is willing to do it with the lights on, becomes less inhibited with age and experience, talks about sex with other women and will brag about how good you are or even how horny you are, only cares about size if it's really dinky, is willing to do what she can to turn you on or help you get a hard-on, will give you a hand-job in the car but is generally uncomfortable with a lack of privacy during sex, will do it in the shower or standing up with her clothes on, wants to be told she's beautiful or sexy, is willing to give and loves to receive massages, likes a bit of verbal foreplay, likes kissing, doesn't care if she sometimes doesn't orgasm as long as you don't make a big deal out of it, is willing to compromise on frequency.
If your W isn't even in the ballpark of the woman I described, your sex life probably sucks and it's not just your opinion or relative to your high drive. You are almost certainly having lower frequency and lower quality sex than the average guy in the U.S.A. in the 21st century. If your wife doesn't recognize this fact she is either delusional or practicing a stubborn form of self-deception.
This tirade wasn't just meant for you, Dave. I'm just getting a little cynical about all the psycho-babble even though it can be helpful. Sometimes I just feel like shouting "The emperor has no clothes" or "Sex twice a year is abnormal" or "Wearing a frumpy nightgown and whining is a clear attempt to avoid sex" or "A lot of guys would love to have a wife with a high sex drive".
"Tell me, what is it you plan to do with your one wild and precious life?" - Mary Oliver