I agree with you fully regarding specialized champions and such, I guess I just saw the addition of Pariahs as a way to fix things without introducing new universal rules. Necrons would benefit more from Stubborn or "They Shall Know No Fear" or whatever the rule is nowadays: they say that fluff-wise Necrons have a leadership rather than fearlessness because sometimes it's logical to run away, however if fleeing from melee is fatal 90% of the time, it no longer becomes logical to do that, especially when there are other ways out a turn away (I mean, staying in combat with the Daemon Prince is 100% fatal, it's true, but if you stick in there for a turn, chances are good of getting teleported out by Monolith or Veil). On that note, let's agree to scrub the Pariah leader deal unless we're talking about specialized squads (like my first idea). Generally speaking, though, I wouldn't mind seeing Necrons stay in completely uniform teams, the mixed squad was just what I opened this thread on.
As for Tomb Guard, you know...as the discussion has gone on, I have begun to think that Tomb Guard really does sound like an infantry model, not a spyder variant. I propose that we call my mini-spyders to Spyder Escorts, and treat them differently, and create an all new unit called Tomb Guard more after your vision (though I still intend to sink my rule-hooks into them, hope you don't mind). So, that said, here's how I'd break the one idea into two.
Spyder Escort (may need a better name)
WS:2 BS:2 S:5 T:5 W:1 I:2 A:2 Ld: 10 Sv:3+
Unit Composition: 3-5 Spyders as a retinue for the Lord
Wargear: Two massive claws
Special Rules: Retinue, All rules for the Tomb Spyder, Modified Scarab Rules, Fearless, Monstrous Strength, Expendable
Expendable: The Lord cannot leave the retinue using usual movement, but because he is so much more important than his Spyder bodyguards, he can--in times of need--opt to teleport away from the squad. Also, their fearlessness does not confer onto him; he uses his own leadership for morale and pinning tests. Should he fall back from combat, his body guard will remain locked in melee to ensure his escape.
In this case, they can still function as a useful retinue, and your Lord becomes a hub for the Spyder ability as well as the Resurrection Orb (typically a Lord and Spyders would accomplish this better, but sometimes you will have used up all of your Heavy Support slots, or you may just want something more survivable...even with only 1 Wound, five of these guys will be much harder to kill than a Spyder, and they'll be protecting your Lord to boot). As you've previously mentioned, 50 points is too steep considering all they do is take abuse (something that the army does notoriously well already), so in this case, and after taking them down to one wound, I figure they might only be 25-30 points a piece. Let me know what you think.
Tomb Guard
WS:4 BS:4 S:5 T:5 W:2 I:2 A:1 Ld:10 Sv:3+
Unit Composition: 5-10 Tomb Guard
Wargear: Warscythes with in-built Gauss Blasters
Special Rules: Retinue, Necron, Steadfast Protection (a good counter-balance though to be fair, our crappy initiative means the chances of sweeping were never high)...maybe Slow But Purposeful, to stop them from being seamless assaulters.
This unit is very tricky. I really like them aesthetically (sort of a more formal and ritual Immortal squad...probably more impressive garb and bearing), but for gameplay they'd be very easy to overpower, on account of being a squad that's as good at combat than Pariahs, but which can also teleport. Originally I gave them two attacks, but if I want them to have warscythes I can't do that (unless our new 'dex gives us such a unit and waives the 'Necrons are weak against good armor' policy...which honestly isn't a terrible policy, I've considered it our main weaknesses for years). Anyway, as they stand right now, they've got monstrous shooting, good CC ability, extreme survivability...the re's just no way they won't be terribly expensive. It's a squad the Lord can keep central to the line or go teleporting around to great effect, so I'm thinking Pariah cost at least for these guys.