Multivitamins is an interesting thought I've never pondered.
The only time I added any additional elements to my plants is when I was growing squash. I bought some Pro-Tekt silicon solution. I'd read you should add that the cuke family for better yield. It didn't help. they just wouldn't produce for me. Reflecting back, I believe it was more an oxygen starvation situation. I haven't tried to grow them again though.

That's what makes sewage sludge grow plants so good...all the un-digested multi vitamins! Seriously I did read an article somewhere saying that was so and have seen the remnants in the sludge with my own eyes. Mom also always adds vitamins to her outdoor tomato pots and always has great tomatoes!

Wasn't going to bring this up here but I am doing a test in a airlift bucket. Two cups of compost for bacterial starter and 1oz per gallon of a liquid multivitamin and mineral supplement meant for people. One tomato plant...

I know a lot of the additives have vitamins and enzymes and carbohydrates - this is stuff plants use and make theirselves but if they are readily available it's easier for the plant to thrive - that's what I've been told and from above it seems like there is something to it.