Re: how much power is worth having, it depends on your lifestyle and other preps. I prep to be comfortable during hard times, not just to scrape by. But it's probably worth getting at least one solar panel and battery so you can charge cell phones, rechargeable batteries for flashlights and radios, etc. That's a pretty minor investment for a pretty major capability.
I'm a data-driven decision maker, so I start by addressing the most likely events first. History shows that I'm much more likely to experience short power outages than I am to see full-on social and government collapse--events where access to gas never goes away, but having a generator would save me a lot of trouble and money.
So I bought one, and now I can stay comfortably at a damaged home and not leave it vulnerable to looters, even running a small A/C while I make repairs. It has already paid for itself just from the frozen food I didn't lose during storms. (We buy in bulk when things go on sale; consider it a financial prep.)
Also, we lost power for a few days during Hurricane Matthew, and I used the electric griddle to make a huge meal of bacon, eggs, pancakes, etc. Then we plugged in the router and streamed movies while we charged the phones. Used the microwave every day, too. Showing my kids that a little bit of planning can make you comfortable during hard times was worth the investment in itself.
And if we ever get to the point where I can't get gas, then I'll just do without like everybody else. I didn't throw out my wood stoves when I bought the generator.