If they take the endless horde route they would need some kind of weapons platform, imho the monolith would gain more not less fearfactor if it became a source of new necrons rather than a heavy weapon toting killer.
A bone giant style walker would be perfect as heavy option, maybe let it join squads and confer a shield - it gives nice images of a towering weapons platform protecting a necron squad.
How about Gaus wepons having some stacking effect instead? meaning the more successful hits by one squad the harder the hit. It would mean more dice = more chance (just like a glancing on 6's) but would also mean smaller squads won't be effective even with cheesy dice rolls (I hate to see anyone, me and opponents get ballsed by dice rolls).
I am no rules balancer but something like each hit on a vehicle confers +1 strength to a combined hit maybe, that way a whole squad of necrons on a vehicle will have a chance for a glancing or penetrating hit, but reduced strength squads no chance.
On the lord note, I would make them very strong and give more upgrades which area affect help regular necrons (or necrons of the same type - detroyer body, wraith body lords

) then make it such that the lords can't resurect through a monolith - this would make the lords hard to kill, but the key to the army, much like tyranid synapses should have been.
The phase out rules could then be removed and simply make the lord and functioning monolith essential to necrons success.