I'm wondering if I should use Apple Photos for my iPhone photos. It only shoots in 8 Megapixels. Does LightRoom really enhance photos of 8 pixels that much vs say a 16 or 20 Megapixal camera?
There is no program that really can do this. No program can add 'real' information that has not been recorded whilst taking the shot.
It depends on what you mean by "greatly improve".
8 mp is more than is needed for a high quality 8x10 inch print. However, there will not be much room for cropping.
LR is certainly able to edit your photos to make them "better".