“Pious exercises” were endorsed by Vatican II:
70. Pious exercises are typical expressions of popular piety. In origin and content, in language and style, in usage and subject, they greatly differ among each other. The Second Vatican Council gave consideration to pious exercises, reiterating that they were highly to be recommended(Cf. SC 13; LG 67), and indicated those criteria which authenticate their legitimacy and validity.
In Lumen Gentium, the concerns are “narrow-mindedness” and “gross exaggerations.” But it is interesting to note that the Constitution on the Church is also concerned for the ecumenical impact of Marian devotion. We blogged about it here.
The other constitution mentioned is concerned, as you might expect, with harmony with the liturgy and leading people to a deeper experience of the Mass and the sacraments, a principle echoed by St John Paul, also citing “conscious active participation” as he did so:
71. In the light of the nature and of the characteristics proper to Christian worship, pious exercises, clearly must conform to the doctrine, legal discipline and norms of the Church(Cf. SC 13). Moreover, they should be in harmony with the Sacred Liturgy, take into account the seasons of the liturgical calendar, in so far as possible, and encourage “conscious active participation in the prayer of the Church”(John Paul II, Homily at the Celebration of the Word in La Serena (Chile), 2, in Insegnamenti di Giovanni Paolo II, X/1 (1987), cit., p. 1079).
Participation can’t be avoided as a conciliar principle, a major one. The full document, the Directory on Popular Piety and the Liturgy, is online at the Vatican site.