In the reality of the situation the Kelvin faced, there was no time for emboldening speeches...by either Robau or Kirk. The most motivation Robau could provide was to Kirk on the way to the turbolift, and then at that, they were standing orders. Robau didn't know what they were about to face...how can you embolden someone against the unknown, especially when the unknown is clearly superior in tech and warfare to your own ship in every possible way? All you can do is give standing orders at that point. There was no help anywhere nearby, and none on the way. Robau knew it, and there was no sense in hiding that fact from his first officer, who naively thought otherwise until rebuked by Robau. At least Robau does not lie to his officers.
There was some time for a brief inspirational speech by Pike just before they left spacedock. "The maiden voyage of the Enterprise deserves more pomp and circumstance than we can afford right now. Her christening will just have to be a reward for our safe return."
And then by Kirk himself:
"Either they're going down, or we are."
Short, simple, and sweet.
I think the best inspirational speech I EVER heard was in StarGate SG-1, by O'Neill. "Anything inspirational you guys may have heard in your lives...now might be a good time to remember 'em."
The second best would be (and yes, this largely was a speech to embolden the good guys against the technologically superior unknown) from Independence Day, by the President.
And then, there's MY emboldening speech, which works for known and unknown situations:
"Anything I might say at this point can be taken with a grain of salt, or regarded as a load of hot air. I ain't gonna lie to you guys....we're probably gonna die. So until we win this thing, just disregard everything I've said at this point! Let's get out there and win this thing! If we do win....y'all can buy me a round! If we don't, well, you can get me in the afterlife!"