The difference is really in which shoes I'm wearing. Heels = dressed up, no heels = dressed.

dress up for a photo party , or everyday dress clothes for exercise mowing the lawn or anything.

Dressing up is putting more effort in creating harmony and concordance with events, going for sympathy.

dressing up for an occasion

nothing

dressing is for getting through the day, it's for me
dressing up is for other people, generally

Dressing is putting on an outfit for the day without a second thought. Dressing up is coordinating an outfit that serves a purpose. Are you a teacher today? Are you a tennis player? Are you going out with friends?

Dressing up is dressing for an occasion

Usually the mess on the bed. Getting dressed is a far less involved process. It helps to have few options -- it makes getting dressed up far tidier.

the level of femininity.

My default is on the more "dressed up" side of things. Dressing up for me is doing more with my hair and makeup than usual, maybe. Or wearing more jewelry.

Dressing is simply putting something on . . . dressing up is making an effort to make it look stunning.

Dressing up = time-consuming and discomfort, happens on occasion
Dressing = everyday practice

Depends

Dressing is when you're dressing for yourself and dressing up is simple when dressing up to show off

Dressing is just for any day where you can go anywhere wearing something "normal", but dressing up is when you put more effort in your outfit and it looks more dressy/fancy. Dressing up is more rare.

"Dressing" is a step above "getting dressed." To me, dressing involves putting some thought into a cohesive outfit the night before to make sure I look well put-together. After dressing, I'll put at least a little effort into hair, makeup, and jewelry.

I 'get dressed' on days when I don't plan to leave my house, and that's really just about covering myself.

I rarely have the opportunity to dress up, but it involves bold choices. Floor-length dresses, short dresses, and false eyelashes. I often try to coordinate, or at least not completely clash, with my partner if we're dressing up.

Dressing is utilitarian, dressing up is decorative and to an extent more consciously performative

Ok, Dressing is to cover your Body with garments so you are not naked.
Dressing up means to me selecting garments and putting them together for a Special occation.

there's none.

I hate, loathe and despise dressing up

yes

Dressing up is ocations like party, wedding and stuff, just dressing is a daily routine.