Outside of Holy Mass, the Rosary is the most heavily indulgenced sacramental
of the Church. There are indulgences for every aspect of praying the Rosary,
like holding the beads of a blessed rosary while praying it, for praying it with a
group of people, for praying it in the presence of the Blessed Sacrament, etc.
But with all these indulgences, it is a conspicuous fact that JPII did not provide
any indulgence for the Luminous Mysteries. Nor did he ever state that any of
the existing indulgences for the Rosary apply to this innovation. As I recall, JPII
never talked about indulgences at all, except for one occasion, when he said
that the Church was opening her treasury of indulgence for anyone who would
go to confession on a certain occasion with the intention of receiving this special
indulgence, it would eradicate all of their temporal punishment, like a plenary
indulgence, for their past life. I forget which year that was, perhaps 1999 or so.
So if you're interested in the Rosary indulgences, don't bother with the Luminous
Mysteries. If you're with a group who's praying it, it's probably best not to make
an argument about it, or to get up and leave, because they'll interpret that as
you being "hostile to the faith," or whatever. What I do is just think about the
Joyful Mysteries instead. Nobody needs to know what you're thinking anyway!
You could even go so far as to offer your Rosary for the conversion of those with
whom you are praying! But you can't really tell them that. Just keep it to yourself.
Look at it this way: at least they're praying the words of the Rosary, and they
might get an indulgence -- because they're praying it with YOU who are thinking
of the indulgenced mysteries!! There is one provision that if you can't somehow
meditate on the mysteries, you can still get an indulgence when you pray the
Rosary with someone else who CAN meditate on the mysteries! But I'm not sure
of the intention requirement for that.