Mask considerations, other than heat and cold, include the diminished ability to see where you're going -- certain areas of the city exist under looser Pershing County building codes (hence the presence of both Pershing and Washoe County sheriffs) and as such are not liable for exposed rebar, tent ropes and variances in setbacks from the roads. Several years ago a friend wearing a Mexican wrestling mask (and perhaps a bit high on life) rode his bicycle directly over an unmarked pile of lumber with, thankfully, no serious consequence. But it could have bummed his week horribly. Nothing like falling on rebar to put a crimp in your style!
Visibility on the playa is one of the key elements to anything you wear -- always carry a light source at night and note that while LED's make YOU visible to others, they don't do such a great job at projecting a beam of light that really illuminates. One art project two years ago consisted of windswept Australian eucalyptus trees mounted on a burn platform in some particular shape. The jagged tree branch ends wound up at about head height and there was no light or warning -- during a mild dust movement (no real wind, just drifting powder) I rode into the installation and nearly impaled myself on said branches. Don't override your headlamp!
I haven't seen much in the way of masks either but they certainly do get used and I can recall a lot of saucy, sexy folk wearing nothing but masks. Most of the masks around our camp tend to be handmade -- a lot of the fire dancers have built headgear for their routines incorporating animistic or fire elements. Depends where you go and what the vibe is -- who are you today? Just try to incorporate some safety (lighting) and your own vision needs into the outfit.