Whether a lens is ‘worth it’ really comes down to what you want to do with it. The f/2.8 is more expensive as there are usually more glass elements, etc. incorporated into its design. But you’ll get double the amount of light to the camera’s sensor compared with f/4 (sharpness can also improve at the same aperture but it’s a long story!). So for sports action/low light photography, it’s generally a winner. However, the question here is really whether the additional expense is worth it? Only you can answer that question! Good luck.
Whether a lens is ‘worth it’ really comes down to what you want to do with it. The f/2.8 is more expensive as there are usually more glass elements, etc. incorporated into its design. But you’ll get double the amount of light to the camera’s sensor compared with f/4 (sharpness can also improve at the same aperture but it’s a long story!). So for sports action/low light photography, it’s generally a winner. However, the question here is really whether the additional expense is worth it? Only you can answer that question! Good luck.