I'd avoid scattering daffodils or scilla in lawns, the foliage gets unsightly as it dies back, and makes mowing the lawn difficult. One large mass planting would be easier to care for, but you'll still have to deal with the foliage. I too have naturalized them among English Ivy (not my choice of groundcover
it was inherited!), also have several areas of Vinca Minor (periwinkle) where daffodils, scilla and other taller spring bulbs are naturalized - very pretty and the foliage dies down into the ground cover.
I like crocus, winter aconite, snow drops and muscari for naturalizing in lawns. The flowers look wonderful peeking out of the lawns, and the foliage dies back before the lawns need mowing. I'd save the daffodials for naturalizing in ground covers or among other plants like daylilies, that will hide that nasty-looking dead foliage