I absolutely think that sex is a good barometer for a happy marriage. And that comes from someone that's been happily married for 25 years this year.
What happens during good sex? (Other than orgasm of course) Trust, intimacy, vulnerability, curiosity, kindess, communication, bravery, openess...all of the things that make a great relationship great, right? Only compressed...When one of them is broken, the relationship is broken, and that can often be quickly seen through the lack of a happy sex life.
If you're spending more time working on your relationship than you're spending getting naked, then you need to stop and see which of those things are broken, figure out how to fix it, and then get back to the business of 'getting busy' again...
Money? When you're getting laid on a regular basis, who cares about money?
But truly, when the rest of your life is firing on all cylinders, as shown by a healthy sex life, then talking, and planning to solve the money issues really aren't that big of a deal...
When you hear "Sex isn't that big of a deal, you need a relationship built on more than a roll in the hay..." that's partially true, but when you hear sex described as "just a roll in the hay" then I guarantee you that they're doing it wrong..it's truly much, much more than that..
If your sex life is boring, then you need to figure out why you're uninterested in spicing it up for your wife? Heh, yeah..you're pissed because she won't spice it up for you, right? This is a 'you get what you give game', it doesn't work the other way around. If your wife feels loved, sexy, appreciated, desired, then she's gonna wanna rock your world...if she doesn't want to rock your world, figure out why she doesn't feel sexy and fix it...
See, all of this is easy!! Ok, not so much..but it is doable. And the good news? The steps that you need to take to fix your sex life are exactly the same steps that you should be taking every day anyway, just to have a happy life. They're just more easily seen when viewed through sex...but isn't everything?