Your course of action really depends on how much work and effort you can put into the expired domain. If you're barely able to maintain and optimize your current site, you probably want to just 301 redirect the old site (note: see my amended comment above about the link value not likely to be passed). If, however, you're more creative and have some time on your hands, you can try your hand at crafting a microsite. If you really know your stuff and are experienced at making money off various websites, you'd probably do well with the third option.
What if we replace “bitcoin” with “ripple” in all these examples? SellRipple.com? RippleGiftCards.com? Ripple.network? Ripple.us…etc. You get the picture. There are a 100 of these on NameBio + the keywords we got from the Google Keyword Planner, that’s hundreds of potential high-value domains right there. The thing is, we’re only scratching the surface here. According to Wikipedia, there are over 1,300 cryptocurrencies online as of January 2018.
Premium Domain names are domains that are already registered, but are available for sale at a higher price. Sometimes it will be an individual selling the domain, or it could be the domain registry (Like Donuts Inc. or Radix) selling their top quality inventory at a higher price point. These domains can be priced anywhere from a couple extra bucks to millions, depending on the domain name, the level of interest, or the amount of traffic it organically receives.
The domain name industry is quite similar to the real estate industry in a lot of aspects. There are end users, brokers, consultants and domain flippers or “domainers”. Domain flipping works similarly to buying a house, renovating it (or even sometimes just sitting on it) and then selling it again at a higher price point. The gist of it is: you’re purchasing a domain name and betting it’s worth (or will be worth) more than you paid for it. If you’re right, you get a nice paycheck and move on. Those who make a living out of this just rinse, repeat, and scale.