I'm of the opinion that you are mistaken in some of your beliefs. The Monolith's particle whip won't help you with 2+ saves most of the time, it's only effective against power armor. Also, the point I made to you was indeed about shooting. If you need me to run the numbers, I can, the fact of the matter is that regardless of toughness, if 1850 points of Space Marines, IG, Tau, Chaos, or any other army semi-capable at range manages to kill ten soldiers at a time(not unusual at all at those points), it won't matter that you have a Monolith. The 'within 6'' rule still applies, so if your squad of Immortals catches most enemy heavy weapons at once(which they will if your enemy is smart), and ten of them fall, you're looking at losing four or more straight up without WBB, unless you crammed them together, in which case you're likely to have lost more than ten.
As to 2+ saves, your only real strength comes from the Deceiver and the Heavy Destroyers. The Heavy Destroyers cost 90 points more than the Deceiver, but the vast majority of 2+ saves that are detrimental to you come in the form of close combat opponents, which the Deceiver is equipped to handle on his own. This means that your Heavy Destroyers aren't all together necessary for your battle plan. Furthermore, they only handle a few different sorts of opponents, and are less survivable than standard. Heavies have their place, but for your list, typical Destroyers would be better. That's all I'm saying. If you think about it, even if you were facing an all Terminator army, your 390 point investment in Heavies will only kill an average of two or three per turn.
As to the Tomb Spyders, I was addressing a defensive issue that concerns your army. You have forgone a Resurrection Orb because it isn't all that necessary in your army, but they are still highly susceptible to the 6' rule. If you're going to go without guaranteed WBB rolls, you want to at least stock up on models, and your desire to take three massive point sinks in your army is making that impossible.
Also, as far as prices between Destroyers and Predators as well as between Necron Warriors and Marines, you can't compare prices between armies, both types of Destroyers are well priced with comparison to other armies, and that is because the Necron army has rules which makes it foolish to just stock up on the big guns. Likewise, Warriors and Marines function in different ways, which account for their relative costs. Ultimately you'll do what you want, but I feel your analysis is off.
