We plan, but not strictly. We make one pot of soup a week to eat mostly for lunches although sometimes we may have it for dinner with bread and salad. We trade off, this week we had some duck stock left over from roasting a duck on NYE, so DH made a great minestrone out of that.
I usually plan 2 dinners per week that there is enough for leftovers. For example tonight I made a crockpot of ham and beans - will get two dinners at least, maybe a couple lunches from that. Earlier in the week I made a tray of enchiladas - good for two dinners and some extra. Plus we keep veggies and salad stuff in the house, and frozen fish and chicken in the freezer. So that fills out six dinners and I really only feel like I need to plan for two, which is way more fun than planning for six.
Also, sometimes we have free night, no one cooks. We just eat whatever we want, sometimes together, sometimes not.
For me the key is to scan some websites and pick out a couple new recipes that look interesting. I keep the links to these in a folder in my browser so if I am feeling uninspired, I just pick one of the links and make it.