We parked in the DTD lot once to go to World of
Disney store on our departure day. I found the walk from the parking lot down through all of DTD quite a long walk. We went mid morning too, so I can only imagine if we'd arrived later in the day and been parked even further away from the start of DTD. That lot is massive and they fill it from the front to the back, so the later you arrive...the more lot you have to walk through before getting to the far end of DTD to begin your long trek to the park entrance. Between the line for getting into that lot and the long walk, it did not seem that we arrived at World of Disney any faster than if we'd parked in Toy Story, bussed over and done the very short walk to the entrance from bus drop off.
Like others have said, you get 3 hours free, 2 more hours with validation from a DTD TABLE SERVICE restaurant (or AMC theatre)....but after that the cost is $2 for every 20 minutes ($6 per hour, billed in 20 minute increments). And shoot, you'll waste $2 worth just getting to your car from the park entrance, lol.
The regular parking lots cost $15 for the entire day (free for AP holders). So only if you plan your day well, eat at a DTD Table Service (or see a movie at AMC), and don't go over your hours is your strategy going to work. Be sure to consider the cost of the DTD table service meal into your strategy and more importantly the time away from the park..... for getting to your DTD restaurant and eating that meal.
And my teenage daughter watching over my shoulder says "Don't forget you also have to walk through DTD, so factor in the cost of any impulsive shopping, lol"