You touched upon the most important aspect of running and theme parks in general...know yourself and what works for you.
I agree with how vitally important this is.
In 2012, I ran the Wine & Dine Half on Saturday night. I had planned to spend the day at my resort off my feet. After about 2 hours of doing this, I recognized that I was going stir crazy. Sitting around my room thinking about the race was not helping. I decided instead to switch up my plans and go to the parks for a few hours. Honestly, that decision caused my race anxiety to move to the back of my mind and I enjoyed Epcot while making sure that I did a lot of indoor attractions with very short waits and/or lots of time off my feet. A few hours later when it came time to go back to my resort, eat dinner, and change for the race, I was ready. The race went fine.
I've always done the parks before the race and on race day. In my experience, I am far less sore after spending time in the parks post race than when I do races at home with no parks to recover in. In my case, the moving around in the parks helps keep my muscles loose. I've continued this strategy even when incorporating Dopey into the mix. It works for me. That said, keep in mind the following.
1. I never allow myself to spend excessive amounts of time on my feet in lines waiting. Short waits and/or long attractions/shows are the rule especially as the race distance the next day increases.
2. I almost always head back to my hotel no later than 7:00pm. I go earlier if I have not eaten dinner yet. So shorter park days are part of my park recovery.
All that said, I broke both of those rules this year the night before Dopey began. About the time I would have been heading back to my resort for dinner and 5K prep, I instead got in a posted wait of 90 minutes for Rise of the Resistance. 3 hours later, I had experienced Rise of the Resistance 3 consecutive times all with significantly shorter waits than posted. Instead of going to bed around 8:30pm, I found myself in Galaxy's Edge then and still hadn't eaten dinner. I went to bed at 11:00pm the night before the 5K. I followed my usual rules over the next 3 days. Dopey was fine and I even took 10 minutes off my marathon personal best.
While I think this certainly impacted my experience as I was more sore after Dopey than usual and had to skip some attractions in order to save my legs after the extra and very much worth it adventure of 3 consecutive times on Rise of the Resistance, I still had a great time.
Know yourself. And if you cannot trust yourself to have a relaxing day in the parks, then maybe it's better to skip them. But if you can, it can be great fun walking around the parks wearing your medal, talking with other runners, and regular park guests.