Yes, mall curfews for teenagers affect shopping in that they increase the rate of shopping among adults who spend more money. Teenagers generally go to the mall to loiter, not to purchase, as teenagers tend not to have much money. This annoys adults, however, and with the teens gone, adults can shop in peace and are more likely to spend.
A lot of people have different schedules, including ones that involve them having more free time at night or later in the day than earlier. Mall curfews would therefore probably hinder their ability to shop in malls, thus impacting shopping there in general. With curfews malls are losing out on money that would be spent at these times.