If you have to ask, then you probably don't need it. That tasks you outlined don't need it. With 16GB RAM and your usage, the iGPU relying on shared RAM won't be a problem either unless you are using memory intensive software you haven't disclosed such as VMs. If you are considering the larger 512GB SSD, I would seriously consider it if I were you. If you are considering the additional storage and the 2.5GHz CPU, than it's a no brainer in regards to cost vs performance.
Those that bash the dGPU are the same ones that have no business using the dGPU. As someone who uses FCPX, I wouldn't consider purchasing the MacBook Pro without dGPU. As far as battery is concerned, the dGPU actually maximizes my battery longevity by minimizing the amount of time the GPU is under load as it is able to accomplish tasks considerably faster than the Iris. When not using software that utilizes the dGPU, OS X, especially El Capitan has been smart enough to switch to the GPU that will use the least amount of power.