I'm guessing you're aware that adding additional days is about $10 a day/person so even if you plan do to some shopping, golf, pool days, etc. you may find it worth while to add a few days to your tickets to offer you either the opportunity to eat in the parks (Epcot has tons of great choices!) or, spread out your park time so that you're not having to go so hard on your 5 park days. We find getting tickets for more days far less stressful than trying to get 'everything' done in one day.
Just my .02