Also, Trumbull was probably wise to suggest the change even if it wasn't for the effects budget. The sequence as scripted is slow and features a silly Raquel Welch moment. It's better that the journey is Spock's alone, and that it's over in a couple of minutes flat.
Well, a proper comparison is impossible since the Memory Wall version was never completed, but I still prefer the scripted version to the final one. Since I'm using my imagination to fill the gaps it probably looks better in my mind than it would on screen, but there would be better character interaction.
And then what's wrong with "Fantastic Voyage"? That movie was released in 1966 (more than 10 years before The Motion Picture) and it was a milestone for special effects. I still remember vividly the first time I saw it (on television). I kept thinking about it for days after. It's a classic science fiction.