Just FYI...Take a look at the price difference between 3 day park ticket and 7 day....about $15 or so....Might be worth it vs. the cost of doing 'other' Disney things (like mini-golf or whatever) to just add that on as I believe it will end up much cheaper.
That said, if you're staying onsite - I would recommend the outdoor sing-a-long, campfire and movie at Fort Wilderness. Warning - if you don't have a car and aren't staying there it can be a bit of a pain to get to and from...but IMO - it is worth it. Free, Fun evening out under the stars....It is only at night though - so I guess that doesn't help with your plan of what to do during the days....