Julia,
If someone opted to do both the Christmas and New Year holiday how much discount would they get (against just adding both trips price together). ?
The way I see it is 3 things should be considered.
1. Obviously Flights would be the biggest saving (once rather than twice)
2. Transfers to and from airport (same reason as 1)
3. Included excurrsions (certainly wouldn't want to do them twice)
Mick