I voted stricter. I usually try to do at least one signature restaurant each trip (if not more). Yeah, it can be a pain to bring along nicer clothes, but you are told the dress code when you make the ADR, so should be able to follow them.
I ate at Jiko in Dec and had the loudest family right behind me. I had made a point of leaving AK early to go back to my resort to bathe, change, put on makeup, fix my hair, etc. The family behind me was obviously dressed in their park clothes. In fact, the mom had almost exactly the same outfit I had on earlier (khacki shorts, Disney T and flip flops). Both teenage boys were wearing flowered board shorts, tank tops, and flip flops, and daughter was wearing a short terry cloth dress over her swimsuit. Dad was wearing a pair of khacki shorts and a Disney Tshirt. Truthfully, I probably would not have noticed what they were wearing, except that they were sooo loud and the mom was wearing almost exactly what I had changed out of earlier, plus you could see the daughter's swimsuit straps under the neck of her coverup. There were quite a few people staring at them, because they were so loud and definitely underdressed.