EXP for an evil altar!?

[Stewbert]

Hey guys planning a "big boss fight" the party is 5 people at level 2. There is an evil altar in the room! The altar does the following; Desecrates the room making undead stronger, absorbs the soul of anyone or anything that dies in proximity of it preventing ressurection and pulses upon absorbing a soul for an aoe inflict light wounds (1D8+1 will 11 for half).

The inflict light wounds trap is a CR2 which is 600 xp, so i could multiply that by 5 for the people its likely to hit making 3000xp, seems a lot but then should I make it more for the additional effects it does?

Thanks for any tips!

[Yue Ryong]

Traps seem to be the most natural way of representing this. I would say that if a thing is in play, it should be reflected in the CR setup... although the trap guidelands only rate multiple target effects as +1 CR rather than [Target #]x Exp.