I heard at the end of a talk by Thich Nhat Hanh earlier this week, which he gave in Vietnam, a woman asked if we are mindful in everything we do, do we need to meditate? Thich Nhat Hanh told her that those who have a high level of mindfulness, constant mindfulness in everything they do, don't need to sit in formal meditation. Being mindful in everything you do is actually constantly meditating during everything you do.
So I agree with you, mindfulness in daily life and formal sitting practice are equally as important. I think with much formal sitting practice, the effects of meditation can spill over into daily activities, making it easier to be mindful in daily activities, permeating every part of one's experience.
"No tree becomes rooted and sturdy unless many a wind assails it. For by its very tossing it tightens its grip and plants its roots more securely; the fragile trees are those that have grown in a sunny valley."
- Seneca the Younger (57 BCE- 65 AD)
"Seek truth in meditation, not moldy books. Look in the sky to find the moon, not in the pond."
- Persian proverb