This is a crazy prediction. It is extremely unlikely that this will happen simply because it depends on a long chain of independent unpredictable events:

"Shortly before the split, people will buy up BTC to hold onto for the long term because eventually the price will go up significantly.  That means a gigantic price spike!"

There is no reason for people to buy a lot of BTC suddenly because of something that will happen eventually. There will be no gigantic spike for the reason you give.

"Then, when the blocks actually do split, the price will start to float upwards until too many decide that's "good enough" and dump off their coins."

Assuming the price rises, then maybe some people might sell, but maybe more people will buy. You can't predict when or if people will dump their coins and what effect it might have.

"A little sustained $0.50 dip after weeks of slow raising will spook everyone into thinking they missed the opportunity to sell off their BTC at top price so there will be a massive dump."

How can you possibly come up with $0.50? Why should such a drop "spook" a large number of people. The price of BTC has recently gone up and down by more than 0.5 BTC and nobody has been spooked into a selloff.

Anyway, your story is full of holes, as are all stories like this. It's an entertaining good story, but it is complete fiction. The problem with these stories that people invent is that they expect everyone to act similarly and simultaneously and they assume people will act irrationally. Furthermore, as I mentioned at the  start, they depend on a long chain of independent and unpredictable events. If the first part of the story is off by just a little, then the entire story is wrong.