From the symptoms you describe, my guess is that you have a small leak from the front or rear valve cover gasket, so oil is dripping down onto the hot exhaust manifold, hence the smell. Replacing the front VCG is easy, but the rear VCG is harder, since you need to remove the intake manifold first. Or you can just ignore it.
I remember reading that it might cause problems switching from dyno to synthetic oil, when the synthetics first came out, but that new synthetics don't have that problem. But I don't know.
Just to be on the safe side, check that the oil pressure switch (low down on the front of the engine, between the oil filter and alternator) isn't leaking. It's a common problem. But you would normally see a small drop of oil underneath the car where you park.