Retrocomputing Stack Exchange is a question and answer site for vintage-computer hobbyists interested in restoring, preserving, and using the classic computer and gaming systems of yesteryear. It only takes a minute to sign up.
Hope we are talking about Feromagnetic data storage mediums (like tapes or floppies). Not an expert in the field but:
Maximum allowable rotation speed?
In general Yes different material means different adhesiveness and structural integrity so you can stress them only up to a point which is different for each material or shape of the medium. This affects the maximal speed and GForce which the medium will survive without degrading. But the speeds used for floppies are too small to even get near these effects. As it is limited by the mechanical properties of the drive and energy consumption and speed of processing. So the answer to this question is not really.
No as you are not mechanically changing anything. The only problem may be the substrate material. That is usually some plastics which can age if exposed to radiation (in long therm) and different material/density means different radiation levels. But too these effects usually surface long after the lifetime of the medium. So the answer to this question is not really.
Sensitivity to external magnetic interference?
Most definately Yes. Different material/density means different size of the head and level of the B field. The higher energy needed to magnetize the lower the sensitivity to external magnetic field. But as experience over last decades show us when you increase the density you increase the auto remagnetization from neighboring tracks/layers. So higher densities lead to better resistance to external fields at cost of lower resistance to data stored nearby on the same medium and usually in favor of the latter (as more dense mediums have smaller life span).