I think Lieberman is more important to the Neocons than that.  

The Neocons have a sort of inferiority problem. They think they're superior people but their ideas are so flakey that prior to 2000 they weren't taken seriously.

Their ideas are still flakey. But, with Lieberman on their side, they could claim 'bipartisanship' for their ideas gaining instant credibility that they never came close to diserving.  

I can't believe that the Neocons aren't lamenting this thought and so are trying to paint Lieberman as a centrist and the forces that are against him as radical reactionary leftist - a true threat to the whole nation.

So perhaps I am wrong, but still, the loss of instant bipartisanship is a big loss to the Neocons and perhaps the first step towards their total banishment from publicn discourse, which having experienced for so long they secretly fear to be a likely event. And it would be nices if that was the case.