Ive lived here most of my life, in both southern and (currently) northern California. Sure, the weather is nice, but my advice would be to stay away unless you are already wealthy or forced to move here for work etc.
If you live in any sort of population center expect traffic to be a nightmare from 6-11am and 3-7pm. Taxes are also some of the highest in the country and poorly implemented social policies continue to increase these on an annual basis.
If you are looking for something in particular that California has to offer, there is almost always better alternatives (see: Oregon, Washington, Arizona, Colorado, Nevada, etc...)
thats exactly what he is saying. Relative to some illegal substances, meth is not worse or somehow more heinous. Part of the problem when many talk about the legalization of drugs is the inherited biases one acquires from paying attention or taking at face value what sources like the media or government say about these substances. The problem isn't that certain substances are much worse than others, it's the fact that these substances (harmful or otherwise) are relegated to the black market.
You could find applications in almost any field, given that there is work done on a computer or have access to one regularly. As for it being a big portion of daily work, I'd guess that most would be technically oriented, similar to those you listed (data science, dev ops, IT)
Anything with a removable cable should last a lot longer, you would only be replacing the cable with any regularity. Depending on your budget, check out IEMs from Westone or Shure: both carry models with replaceable cables and are reputable brands in the recording industry.
Rent control and other government instituted economic controls are what is creating the housing shortages in these popular 'tech' cities. People in general are ignorant of basic economic principals which leads to quotes like the one spouted off by your girlfriend.