God forbid you commit yourself to something intimate and personal with your wife for 100 days.
Yes, maybe sometimes it's a chore but just like anything, you learn to appreciate and respect that. It's the committment that contains the value for your marriage. Just like you commit to your kids, or your job, or running, or paying bills, or even monogamy with your wife. None of them are ALWAYS fun, but you learn to appreciate and value each of them.
Sometimes you'd probably love to get dirty with the girl at work who you know has something for you, or you'd love to blow a few grand on a TV and throw the bills in the garbage, or you'd love to get in a round of golf [beers] instead of being with the kids. But you sacrifice the fun in that in lieu of your other responsibilities and commitments, as shitty as they are.
This is the same idea as the 100 days of sex. Maybe it takes the fun out of sex for a little while, as you contend, but you commit to it and learn from it. Who knows, maybe you'll change your own mind part way through.
I'm not saying it will ABSOLUTELY work, but I think it's worth a shot to see. Start with a deal on a week, and if you both feel wishywashy about it then stop, but if you start to see something [or she does] then try a month, after a month commit to 2, then 100 days...