Indulgences, like the Tridentine Mass have never been abrogated but I cannot recall the last time I heard a priest refer to them. I am aware of the "Enchiridion" (sic) of indulgences but have not seen it in some time. Prayers for the Souls in Purgatory has also disappeared. Is it worth the effort to try to see these things revivied?
An indulgence is a favor granted by the Pope, using his authority, to attach some remission of the temporal punishment due by sins (either partial or plenary), upon the performance of some charitable act.
Since it is a favor granted, these favors can be revoked. A Pope may remove an indulgence. "Abrogation" is not a proper term for Indulgences in general, as no Pope could do away with the concept of an Indulgence. No one has ever claimed that Indulgences have been "abrogated" as some have done with regard to the Traditional Mass.
It used to be that some amount of time was attached to an Indulgence (days, years, quarantines, etc). This was the equivalent time of doing public penance. A quarantine was 40 days. Thus a 7 year partial Indulgence would be the equivalent to confessing and doing 7 years of penance toward my sins.
Pope Paul VI did, however, modify the way the Church approaches Indulgences. Now, instead of time, an Indulgence is either plenary (remits all temporal punishment due to past sins), or partial (remits some of the temporal punishment due to past sins).
Of course Indulgences and the acts of charity and devotions attached should be encouraged. As with all supplementary devotions, however, they should be encouraged as supplementary to the daily prayers that are more obligatory by their relation to our daily life : Morning and Evening prayers, Rosary, Prayers at Meals, Daily Mass.