I guess the question is, "Is it worth the extra hours in the park vs. the cost of a cab?"
My response is that if you expect using a cab vs. DME to allow extra hours (plural) in the park, then you are expecting too much. The $50 spent realistically would allow you to spend at most an extra hour (or even less) in the parks.
Using DME, you will be scheduled for a pick up at around 2:30 p.m. and should be wating for the bus by 2:20 p.m. Assuming that it takes 15 minutes to claim anything from bell services, use the bathroom, etc. that means you need to be at the resort by 2:05 p.m., or so, which means leaving the park by about 1:00 p.m. or 1:15 p.m. so that you have time to get to the bus depot and catch a ride back to your resort.
If you have to store bags with bell services, you will need to be back at the resort and ready to catch a cab by 3:00 p.m. or so anyway, which means leaving the park by 2:00 p.m. This scenario, therefore, buys you about an extra hour at a park.
There are certain specific scenarios that will save you some time in park-to-resort tranportation, such as if you are staying at a monorail resort and will be at the MK or if you are at one of the Epcot resorts (BWI or YC/BC) and will be at Epcot or DHS that day.
The only exception to the above that I can think of to maximize time at the parks and get yourself up to two hours of additional park time is to use RAC for your bags and boarding passes (your flight time would allow you to check in as early as 5:30 a.m.), leave nothing with bell services that you have to collect later, take everything you need to carry on to the park with you and stash it in a locker, and take a cab straight from the park to MCO when you are ready to leave. In that case, you might be able to stay in a park until as late as 3:00 p.m., but what you are able to take as carry-on baggage will be very limited. If you are willing to leave yourself with little or no cushion to account for possible traffic or airport delays, then you could potentially squeeze another 30 minutes in. As noted by a PP, however, this also requires that you are on an airline that participates in RAC. If you aren't on a participating airline, this course of action simply isn't an option as you almost certainly will have to store bags with bell services.