Awhile back, I was asked about wearing tights and I outlined what and when a villain should typically wear. Today I want to go into more detail about skin-tight outfits, also known as "super-tights", spandex, or whatever.
Cost. The worst part about the cost of super-costumes is the expense. If you have a motif, you're basically custom-ordering a new one with your pattern on it every time it gets damaged, which will be a lot. This is why many villains prefer color patterns to distinctive symbols.
Comfort. Spandex doesn't breathe at all. It won't let sweat and body fluids out. This might be rough for mundanes, but for supers - who often have alternate metabolic arrangements - this is a non-issue. What spandex does do is stretch and give, which is something you really need your attire to do.
Appearance. As I mentioned before, spandex will make your toned Stage 3+ body look great. This is important because appearance is a valid tool for distraction, charm, and manipulation. Fuego, the villain turned hero in the 80's, was reputed to have "the abs that launched a thousand ships", and he worked it for all he was worth.
Biology. Wait, what? Yes, really! Many supers have powers that radiate directly from their cells. The effect past the skin is very short - a few inches at most, more often than not. An example is the field radiated by teleporters, or many kinds of defensive barriers. You can learn to push this field further - and usually do, unconsciously - but it can be exhausting in the long term. The solution, unsurprisingly, is to wear thinner clothes and not carry things in your hands.
Protection. Basically nil, but by the time you're ready to wear spandex for the reasons given above, you usually shouldn't need much protection from conventional weapons. My personal rule of thumb: once being shot at point-blank range feels like being punched in the chest, you're bullet proof and can switch over to spandex. Before that, wear body armor. Seriously.