Decorativeness
The presence of non-essential visual additions that heighten emotional or aesthetic response beyond a form's function.
In practice
Decorativeness is the amount of added visual detail that serves feeling or beauty rather than function: ornamental borders, flourishes, patterns and embellishments. It is not a fault in itself; a wedding invitation or a chocolate box often benefits from it. The design question is fit and degree. Decoration should support the message, not bury it, as it does when an ornate frame makes a timetable hard to read.
Often confused with Pattern
Decorativeness is non-essential embellishment of any kind; a pattern is a structured repeating motif, which may be decorative or purely functional.
Try this
Make two versions of one greeting card, one plain and one decorated, and ask which suits a formal occasion.