I am also in the process of building a Necron army and am fairly new to 40k. I notice that your list is greater than 1000 points, so I guess you're not using all of these models at once.
Even though the Monolith is an awesome supportive tool (I assume you're not planning to deepstrike it), this army is only able to fire a maximum of 20 shots at a comparatively average 24" range while it advances thanks to the Immortals, if you use the full squad. At 1000 points a unit of 4 Destroyers (200 points) would be useful in place of the Monolith, providing 12 mobile shots at S6 while your warriors get into rapid fire positions. Next I'd consider removing a few of the Immortals to free some points for a Veil on your Lord to teleport units out of assault, meaning you don't entirely lose the Monolith's utility. By splitting your mobile shooting into two units (Immortals and Destroyers) rather than concentrating it in a single large unit of Immortals you gain a lot of flexibility. The Wraiths will probably need to go to accomodate these changes, but the loss of three close combat models for greater shooting capacity isn't a bad thing here, and there's no reason you can't use them in 1500 point games.
This leaves some points to do as you wish: Use a Wraith to capture objectives, replace an Immortal or two, bulk up your Warriors, or add a unit of Scarabs. It's up to you.
