Coming from an internet marketing back ground; the name of the game in virtual real estate is traffic. If you have a lot of traffic to your site then you have a higher Alexa ranking. A high Alexa ranking means that you could possibly resell the site for a profit.
That being said build that traffic stream and thus your rank can take a lot of work. To rank organically (non-paid traffic) on Google you need to be adding quality content to your site regularly. You can add some back links (links on other popular sites back to yours) but in the last few years Google has changed their algorithm to place less value on this. From experience building traffic can add hours to your work and thus kill your pay per hour.
Additionally, a lot of the pay for traffic options out there are beginning to be discounted by Google and the other search engines because they are realizing that most of the interactions being recorded are not legitimate.
Finally, there are a lot of professional internet marketers out there doing the same thing so the market is flooded with hundreds if not thousands of people cramming the same niche markets. Just to give you an idea a Google search for "real estate investing" returns 74,700,000 results. that is a lot of competition. Now if you wanted to start a blog it can take 2-5 years for you start growing a following and making a part time income from the blog.
I hope this gives you an idea of the virtual marketplace and the key take away is for every Amazon, Facebook, Ebay, etc. There are thousands and thousands of other sites out there that make little to no money.