[knottyb0y]

A monk would add: more DPS to your group in general, and great pulling ability (sneak, throwing stars and of course FD).
A necro would add: DPS(pet, dots, nukes), crowd control (screaming terror and roots), and backup-backup healing.

Monks are a very fun class, and a well geared monk should outdamage a necromancer. But if you are working with a shaman/paladin duo, you probably are dealing with long-ish fights anyway.. This would maximize the necromancer's damage to mana utility because more dots would sit on a mob for longer.

Personally I think adding a necromancer would mean your party would be able to do more things, particularly in dungeons. The paladin, with lull, can be a powerful puller. Monks are good at feign splitting but it takes a lot of skill, patience and work.

Either way you are in for some fun.