SinCrisis, to answer your question, no. One has to keep in mind the various nutrients. Plants do not require very much of any one of them, and they must all balance the light. This is why, in a low-tech natural system, a comprehensive fertilizer is considerably more economical--it takes so very little.
First, a comprehensive fertilizer like Flourish does not have so much of any single nutrient that overdosing of this or that nutrient can occur, because it is highly unlikely sufficient amounts of any one nutrient will be available in the aquarium from other sources. At least, not those that could cause trouble (iron, copper, manganese, etc). Even most fish foods today do not contain much potassium [or is it phosphorus, sorry, memory blank out] that is said to cause algae troubles. And most water supplies have limited if any heavy metals (iron, copper, zinc, manganese, nickel) and we use water conditioners that detoxify these anyway.
Second, some plants can store a limited amount of nutrients. Slow-growing plants do this, like crypts. And here again, the "excess" is not likely to be that great.
Third, plants detoxify metals. There is obviously a limit to this, but they do it, along the same methods as the water conditioner. We call it "taking up" as opposed to assimilation. Plants assimilate copper as a nutrient, but in excess they take it up and thus detoxify it.
To the next point made by redchigh, we would indeed have to test for every one of the 17 nutrients, and that is not only laborious (and well nigh impossible for those of us without scientific equipment for so many of the micro-nutrients) but un-necessary. Nature has a way of balancing things, provided we do not tip that balance. Which is one reason I do not adhere to the EI method. First, I can't understand the logic of dumping nutrients into the tank and then doing a massive water change to remove some of them, which is the basis of the method. This is much more likely to create the problems mentioned in the initial question.
Last comment on nutrients in the water versus soil. Plants can only use nutrients dissolved in the water--they cannot assimilate nutrients from soil. The nutrients in the soil must get into the water in the substrate in order for the plant roots to assimilate them. The same works in land plants, which is why hydroponics is so successful [terrestrial plants cultured in water without any soil]. The soil is simply the storage place of the nutrients. But the nutrients can just as well be added to the water column to make their way down through the substrate (if it is not compacted) and thus be assimilated by the plant roots. And of course there are plants like floaters and non-substrate rooted plants that have no use of the soil or any substrate at all as far as nutrient assimilation is concerned.
Byron.