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.

Dressing is what you do every day. Dressing up is special somehow. It’s up a step from the usual, whether up into the halloween spectrum or into elegance.

I chose the outfit vs. someone else chose the outfit.