I see no reason not to believe that the plagues actually happened. But that doesn’t mean they don’t have many layers of meaning.
In Scott Hahn’s “Understanding the Scriptures” (p. 134-135), he points out that the first 9 plagues are grouped in three groups of three. “In each cycle, the first two plagues come after a warning, and the third with no warning to Pharaoh at all.” I’m not sure what the significance of that is, but it is interesting.
I believe I saw Hahn make the parallel elsewhere between the ten plagues and the Egyptian gods. Each plague targeted one of those gods, culminating in the death of the first born (for which Pharoah’s first born would have been considered a god).
Initially, Moses simply asks for Pharaoh to let the Israelites go into the desert to make sacrifices to God. These sacrifices were “abominable” to the Egyptians because they were to sacrifice the animals that the Egyptians worshipped.
The 10 Plagues (and, indeed, the whole Exodus story) is about freeing the Israelites from attachment to other gods. God is trying to show them that He alone is God; he wants to root out the idolatry from their hearts. Note that this did not happen overnight (if it ever happened!). The Israelites had been in Egypt for 400 years, after all. God was teaching them to disavoiw themselves of these Egyptians gods through the plagues and through the animal sacrifices He was requiring of them.