There are so many variables involved and options to choose from that it can make you dizzy trying to sort it all out. We've learned that what works for us varies with each trip. It depends on whether both kids are going, how long we're staying, whether we really need park hoppers in order to maximize our time, and how much we feel comfortable spending at that particular time.
If our DS opts to stay home, we can comfortably fit into a value room. If he goes, we'll need accommodations that give us seperate beds for the kids.
If both kids are going, we need accommodations that provide each with their own bed. Onsite accommodations that give us the three beds we need are usually more than we're comfortable spending so if both kids go, we'll likely opt for a condo offsite even tho a value room onsite might have been a little cheaper. All four of us in a value room just is not very comfortable. One thing we usually will spend extra for is park hopping. We've never been able to stay more than 7 nights cause that's as long as DH can take off work. Having park hoppers helps us maximize our park time to make up for not being able to stay longer.
We have gone for shorter trips (3 or 4 nights) and always stayed onsite for those. We figure we can stand just one room for those few nights and having the onsite perks like EMH and the option to split up can make a lot of difference on such a short trip.
If a discount is offered, it may figure into our decision but
free dining never does because we can't go at that time of year.
If you're on a budget, you just have to figure out which elements (like park hopping, bus service, full service restaurants, etc) are essential for you to really enjoy the trip and which elements you can do without and still have a good time.