Having a good ground plane for the antenna is important. When I use to fix RF transmitters and antenna tuners in the Navy, I often encountered corroded connections for the grounding connection. At a non-shipboard site I once worked at, the ground plane was created by burying a braided wire mesh configuration, it was like a star configuration. Ugh that is not a very clear description is it? Basically it was a ground plane mesh buried about 1 foot in the dirt with braided wires going out away from the dipole. There was one attached wire that came out of the ground and was used to attach to the antenna ground connection.
Anyways, the connection points to this mesh would often be a big source of problems and really jack up the VSWR. I once had one so bad the VSWR was over 2.0, so with that long winded description, my point is, grounding is real important and can degrade system performance over time, and weathering can be a real culprit.
I can't remember what the ground mesh thing was called or I would try and locate a reference.