I've always understood that studies show that too much sleep can actually make you feel more tired, just like not enough sleep does - even for those without MS. Are you sure the effects are "MS symptoms" or just the normal result of too much sleeping? Even for 'normal' people it takes a while to wake their body up after a night's sleep or a long nap. An extended rest - like for an illness or injury - really slows you down and requires you to build your strength back up. I work full time and I've noticed that a lot of the people around me complain more about fatigue than I do.
Personally I seldom blame MS for anything until I've eliminated every other possible cause, so very few of my problems turn out to be due to MS.
I figured out a long time ago that regular 8 - 8-1/2 hrs sleep is perfect for me and then I rarely need a nap. Too much more (like 9-10) or too much less doesn't feel nearly as good. So I don't do it. I bet it works the same way with non-MS people.
Everyone's metabolism is different and each must figure out what works best for them, but I think 7-8 hours of sleep a night is generally accepted as best for optimum restoring of one's body and mind.
The bottom line: I have no idea if too much sleep affects one's "MS", but it never matters to me whether a problem has to do with MS or not anyway. If something doesn't feel good, then I stop doing it that way.
Good health and energy to all!