May have Lucius convinced that he is Voldemort

Not much use if he hasn't figured this out.

Is an almost-perfect Occlumens

If he is, I don't think we know this. He's at the stage of being able to block veritaserum, and thus probably to put up a block to stop anyone reading his mind, but I don't think we've been given any indication that he's reached the point of being able to show false thoughts to someone attempting to read his mind.

I would add that he knows Voldemort is probably alive. If he were to testify by placing his memories into a pensieve, he could show that the Hogwarts inner circle has strong reason to suspect that Voldemort is alive and behind this plot. This might create a measure of doubt among the Wizengamot, at the cost of probably throwing the country into turmoil, so we can call this the Stupid Sentimental Hero Option.