2005 Altima. ...  valve cover gasket keeps needing to be replaced?

Is it overfilled with oil? Overfilling can cause it to leak through the valve cover gasket. Seeing it on the ground doesn't necessarily mean the oil came from the valve cover gasket. Could have a bad or leaking rear main seal. If you are concerned about your engine misfiring due to the oil being in cylinder one on the spark plug, use a non-fouler.

A valve cover gasket leak has nothing to do with oil in a cylinder. 

Is there oil on the outside of the spark plug? 

Is your valve cover made of plastic?  They often warp. 

I have fixed a lot of Saturn leaky plastic valve covers.

The oil into the cylicer is most likely a leaking valve stem seal. Valve cover gasket failure is often due to a ham fisted mechanic tightening to down too enthusiastically.

In order to absorb thermal movement the gasket has to be able to flex.

I am guessing that you mean oil in number 1 spark plug well. have the seals at the top of the cover been replaced?

The valve cover gasket has nothing to do with oil getting into a cylinder.  The valve cover is simply that, a cover to keep dirt out of the valve gear and contain mist from the oil which is directed to the rockers.  The gasket is there to prevent this oil from leaking out and getting over the outside of the engine.  If yours is leaking either the valve cover is warped or someone has installed it badly.

Find a different mechanic who does a better job replacing the gaskets. Possibly using a different brand of gasket as well. Some **** from China does not last.

The engine is wearing out.  I say replace it.

Oil in one cylinder is not caused by a valve cover gasket.  It will be cylinder/piston wear, piston rings, valve seal, or valve guide problem.  

The external leak will be a gasket or deformed valve cover to cylinder head mating surface.