I find the biggest problem with the spacewalk, as we have it, to be that it's not properly framed as being the suicide mission that it really should have seemed to be. Spock should have no reason to think that his log will ever be recovered, because after he's burned up all his fuel, he discards his thruster pack.
Why the heck couldn't they have made it a 40% fuel burn???? Heck, if they had done that, Spock could have set the autopilot to return him to the ship before making the first burn, just to better make sure that his log makes it out of the orifice. That way, we're also not wondering why V'Ger would bother to spit him back out, especially if the mind meld didn't discernibly affect V'Ger otherwise.
No doubt production time crunch played a role in bringing on the nonsense.