This type of argument does nothing to support a view. Every view has to make some kind of sense, literal or spiritual.
Just remember, His ways are fully above our ways. We shouldn't expect to understand how God will do all that He has said. But I do expect He will do all that He has said.
For me, to read a passage, and then question, how in the world could that ever happen? And to follow up with, That doesn't make any sense to me, therefore, it must not be like it says, This is to me a recipe for error. If there is a textual reason to think that something is symbolic/metaphor/allegory/parable/idiom/type, and if there is something to tell us what that symbol, or type means, that's one thing.
But when we don't have that, when what we have are straightforward propositional statements, without qualifications, without modifiers, I don't consider it to be good interpretation to declare it's not so.
In this case, you are asserting that it's nonsensical that the plagues added to the one who adds to the book be the literally reading plagues of the trumpets and bowls. So therefore, these plagues themselves must not be the events described, such as the trees and grass burnt, or the sores on those with the mark, or the massive hailstones. These descriptions must be symbolic for other things, things that can be shared by those who add to the book. So that it can make sense.
Do I have this right? This is your thinking?
My response is that there are things we may not understand, that may not make sense to us, but that remain just as real and true as they seem when we read it. So in the case of these plagues, yes, they will happen as written. There will actually be fire from heaven, and locust-things coming out of the abyss. And in the case of those who add to the book of prophecy - the Revelation - God will add these plagues to them. If I believe the prophecy of Jesus returning, well, this is written in just the same way. Narrative, propositional, straightforward. And I understand that God is able to plague an individual in these same ways, that there is an experience that He's talking about, and such people are able to suffer in such ways.
To me the most likely parallel in Scripture is where Jesus said that those who knew better will be punished with many stripes. Maybe this additional suffering - darkness, gnawing your tongue in pain - in the terror and confusion of massive hail - in the bitterness of Wormwood - is described in the "many stripes". But in this I can only speculate, as this is not directly stated.
Much love!