I just replaced mine with ones from meek, they are similar to the stock ones as i drive on alot of dirt roads etc so the ones tbowgn sell would have been a bit to hard (nothing negative against them as i have never used them)
anyway the rubber in the original mounts had snapped so the engine was moving around a fair bit, which to me made that car feel sluggish and not as good on cornering. the damaged mounts would also make it difficult to get into/change gears depending on how the engine was sitting at the time, if i was lucky the engine would move a little around a corner and id be able to change gears nice and easy
from my experience, if you go with stock mounts and you do them yourself you'll need access to a press and you need to be careful as they can get damaged quiet easily trying to push them in
so yes, they are important to replace if they are damaged/cracked, if there not damaged/cracked then there no real need to do it