Domain names have been on sale ever since the Internet revolution began during the 90s. Just because some entrepreneurs had the foresight to buy profitable domains before the rest of the world caught up with the trend, doesn’t make them domain hoarders. Domain names are just like the real estate sold in the off-line world. Anyone is free to buy/sell as many properties as one likes if his/her means permit.
Domains are nonmaterial goods. When sold, the only transaction taking place is transfer of domain rights from one user to another. Barring any form of copyright or trademark violation, virtually any domain name can be bought or sold. Generic domain names, such as car.com or computer.com, are not legally protected and can therefore theoretically be reserved by anyone.
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.
Please keep in mind that domain flipping isn’t child’s play. As much as you may want, it isn’t easy to buy and sell domain names for huge profits without putting in a good amount of time and effort. Although there’s nothing wrong in aspiring for at least one big deal per month, be aware that sometimes it takes months and months to sell just a single domain name.
That being said, many things have changed over the years. The days of MFA and quick flips are mostly gone. My advice to those new to domaining and wanting to give it a try is to take it slow, do your research, and if you do purchase a domain with the hope of turning a healthy profit - put some real time into it and build something useful. That way it's easier to monetize and easier to sell.
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.