A few suggestions:
1. Keep your tempo efforts unstructured. When you're feeling good on a run, just pick up the pace to something that is comfortably hard, and just keep going until it feels like enough.
2. Turn all of the data fields off on your watch. If you have no way of knowing the results of your workouts, you won't endlessly analyze the pace and what that means, etc, etc.
3. If you're on strava or uploading your training to some other social media site, set it to private, or don't upload at all.
4. As another poster mentioned, get your Vo2 max and/or LT conditioning in by cross training. Personally, since adding in cross training (roughly 5 hours/week), I've gone from running 17:20 for 5k to 16:30. It allows me to get an extra hour or so of intensity in per week without the additional impact of running, plus I don't care about the results of these workouts, just the effort.
^^It's even changed my mindset to the pain experienced through exercise. When I ride hard, I'm trying to bring on the pain that comes through intensity, rather than trying to avoid it. It makes running races far less intimidating, as I don't fear the pain as much.
5. Maybe try the no-intensity approach for a month or so and see how it goes. The most important thing in marathoning is running economy, and you should be able to improve that with more mileage and strides.