there will not be a "Gavincoin" and an "Adamcoin". Even if the chain splits, and the 1 MB branch survives for a while, there will be just a two-headed bitcoin. Even if you could trade and speculate on each coin separately, you cannot attack one in the market without harming the other.
You are assuming at least two facts not yet in evidence. Your asserted answers to empirical questions carry very little weight.
Your narrow comp sci prof paradigm is insufficient to make predictions which involve dominant socioeconomic factors.
EG, although 1mb spam attacks are cheap, they do nothing to tx paying competitive fees. Making blocks 8 times larger only makes spam attacks [8 times cheap] more expensive, while other trade-offs incur increasingly (superlinear) negative margin returns.