I don't follow this logic. If the market cap grows by 100, all other things being equal (very unlikely), the price per coin will multiply by 100. Only 2 or 3x people will start mining and everyone else will leave the 33-50x profit to miners?
Four things. One, the block reward halving will make mining more competitive. Two, there are only 8 million out of 21 million Bitcoins mined so far. Three, newer mining technologies will produce a 10-20x reduction in power usage per hash. And finally, eventually the price of Bitcoin in dollars won't be particularly relevant anyways, assuming things go well.