Are people with slightly less than perfect vision still supposed to wear glasses and/or contacts?

Should they, yes they should! Many people have perfect distance vision and often need reading glasses for up close. But that can be a pain having to remember to carry reading glasses around and many opt for bifocals to wear all of the time if they need stronger reading glasses. Even if people have a very mild prescription for distance it isn't going to hurt to wear them all of the time, even if your eyes are still good enough to drive without glasses! Many people refuse to wear glasses and will try to avoid them or go straight to contacts. But even if you get contacts it is strongly recommended to get glasses to wear when your contacts are not in and alternate. If you never wore glasses before and need them it is not the end of the world! Get them and wear them with pride as almost everyone will need them during their life! Even if its a mild prescription you should always wear them to your eyes don't strain and give you headaches and that your vision don't get worse! By wearing glasses you will see things that you may have never noticed before, so do yourself a favor and if you need glasses get them and wear them all the time!

Supposed to? It's a personal choice.  

I would offer glasses to anyone who would see even a little bit better with them. It would be up to the patient to decide if it was worth it. Like another person pointed out, for an adult, the only time that "supposed to" enters the discussion is when they can't see well enough to drive. There are times when children might be required to wear glasses even if they thought that they were fine without them.

The only "supposed to" I know of is actually "required to" and that's for driving a motor vehicle.