Bacteria are the biggest argument against grey goo. They already are, they already exist, and they're already everywhere, yet things other than bacteria still exist. They've had several billion years of evolution to work on it too.
They're probably in local maxima, not in any global maximum, but it's also likely that there is no single global maximum given how different the requirements are for using different energy sources.
The thing I would worry about it replicators that use stronger chemical bonds than bacteria do and can eat bacteria but can't be eaten by bacteria. They would probably have to reproduce much more slowly due to higher energy requirements but if they end up eating everything in the long run it might not matter.
Incorporating fluorine in a molecule offers additional flexibility over the more common chlorine and bromine compounds commonly found in natural products. For example, the fluoroquinolone antibiotics are distinguished by their introduction of fluorine, yielding compounds more effective than found in nature.
There are a few fluorinated natural products made by wild organisms, but they are very rare considering the elemental abundance of fluorine on Earth and the high utility found for fluorine in pharmaceutical development:
The strong bonds formed by fluorine, and its formation of insoluble compounds with alkaline earth metals, probably explains the rarity of natural fluorinated products. The fluorinated natural products are no more "dead matter" than other poisons evolved by plants against herbivores, but it's hard to evolve out of local minima that exclude fluorinated compounds.
Not really. Flying faster than the speed of sound without complex supporting industry is not possible. Flying faster than the speed of sound is not sustainable, it is something we have to work very hard to achieve, and the second we stopped trying very hard to do it, it would cease to happen.
Grey goo, on the other hand, has to be self-sufficient and sustainable to exist.
They're probably in local maxima, not in any global maximum, but it's also likely that there is no single global maximum given how different the requirements are for using different energy sources.