Do cell membranes have more phospholipids in one layer than in the other?
Yes there is a difference in the number of phospholipid molecules because of the curvature. This is very evident when there is a lot of bending as in case of exocytosis (see here) but otherwise I do not think there would be an enormous difference in the number of phospholipids between inner and outer surface of the bilayer.

Assumptions:


Cell is spherical
Cell diameter = 1µm (overall)
Thickness of bilayer = 6nm
Width of a phospholipid molecule = 1nm 


Difference in circumference of outer and inner layers = 2π(6nm) ≅ 37.7nm

So approximately 37 more phospholipid molecules in the outer layer in this cross section of the cell. This is just 0.6% of total number of phospholipids in the outer membrane. 

I don't think fluidity will be compromised because of this - only if a layer is overpacked will the fluidity be affected.