I know one person who is part time domain investor he has mre over 10,000 names ( you read it right.. ten thousand).. He parks his domains on different parking sites. He makes around 1000$ a month from all his domains. He sold his domains for over 85K USD last year. if you see the stats- he made good money on his investment last year. Luckly- he got a domain name which is expired for 15$ whcih is fetching him 300$ a day from parked page alone due to a merger of 2 big companies recently.
I would say- Domain Investment is 'Buying a vertual property'. If you get a great name, you can sell it at great prices. Else- It will be a burdon for you to drop it or renew it.
If you can build a website with good SEO, any domain name would fetch you what you want.
Good Luck