An entertaining thread. At the risk of sounding preachy, you should think about the terrain you will be flying over. For instance If you are flying over sparsely settled terrain in winter you should be properly dressed to survive outside if the airplane crashes.
One thing that is for sure is the likelyhood of that one spot of horrible greasy exhaust residue with a hint of hydraulic fluid, transfering to your clothes is directly proportional to the cost of what you are wearing
Cheap and comfortable are the primary criteria for my flying clothes.
BTW I wear a nomex flight suit and gloves when flying my Nanchang CJ6A, but I would never wear it when flying a cessna or piper.