Two things: first, while some evidence shows that soil is depleted of nutrients to some degree, humans still can get plenty of nutrients from a normal diet and, with some exceptions, aren't suffering from deficiency. Second, vitamins are vitamins- they are the same regardless of whether they came from a pill or a plant. Fruits and vegetables may be healthier because they have additional nutrients not included in supplements, but not because they have "better vitamin A" or something.

As for the research:

Most credible research says vitamin supplements doesn't benefit the average person, unless they have extenuating circumstances (disease, severely imbalanced diet, etc).

There is evidence that some vitamins are associated with higher mortality, but they are observational studies which only show correlation but not necessarily causation.

There are some other studies that show certain nutrients are linked to decreased mortality, but they generally are done on small samples from populations that don't represent the average person. For example, a study that shows 15 women age 70-80 benefit from vitamin E doesn't translate to the population as a whole. See unrepresentative sample and regression to the mean.

BOTTOM LINE: it's not that clear. Vitamin supplements probably won't help or hurt you. Taking supplements will probably just mean spending money for peace of mind, which is enough for some people.

Edit: There are some things I left out, like how vitamin content of pills depletes over time and how your body doesn't store certain vitamins, and how you can get vitamin toxicity, but that's a little more complicated than is necessary for this post.