Stay on property and rent a car. You have the freedom to travel where you want, when you want. When you want to park hop and/or resort hop, the longest wait you'll have is however long it takes to get to your car in the parking lot. With the buses, you never know how long you're going to wait. Given how much you're paying for this trip, even if you're staying at a Value, your time is too valuable to waste on variable wait times for buses.
Also, now that Pop Century has Wi-Fi and fridges included, you can discover how close the Targets on US 192 are to WDW and load up on snacks/drinks, saving a TON of cash. The Target on 192 west of WDW is actually closer to the Pop than Target is to my house. It takes less than 10 minutes to get there assuming no wrong turns are made.
Another benefit of renting a car is not having to leave for the airport as insanely early as DME wants to pick you up. The whole baggage delivery bit isn't much of a perk since on my last trip to WDW (2 weeks ago), the luggage had just come out when we made it downstairs to baggage claim. No waiting involved, unlike LAX where baggage claim takes an hour or longer. This gives you more time to desperately cling to WDW screaming, "I DON'T EVER WANT TO GO BACK HOME!!!!!!!!"