There are over more than 3,000 people in the stadium.
What do you think about this duplicated expression "over more than"? Does the redundant wording serve to intensify? Or is it wrong?
Over doesn't work as an intensifier here. Your example sentence just doesn't sound right.
But don't take my word for it: look at the search results on Google Books for this phrase. It's only used in examples like this:
- She'd turned over more than once
- Looking back now over more than half a century
- Smooth solid russeting extending over more than one-half of the surface
- Lozen's story roams over more than just the Arizona Territory
That is, the over is associated with the preceding verb, not as an intensifier for more than.
If you want an intensifier, use one like much, way, or far in front of more than instead, like:
There are far more than 3,000 people in the stadium.
Why not say There are more than over 3,000 people in the stadium. It doesn't tell you anything that There are more than 3,000 people in the stadium wouldn't tell you; but it is idiomatic. The way it is expressed in the question is not.