I am a Realtor and own a number of "city"homes.com and a couple of "city"realestate.com domains. I've licensed a few of the "city"homes.com domains to other real estate agents. I think Adam is correct that it's a narrow market, end users are agents, firms, or homebuilders.
To me, a "city"realty.com has very little value since realty isn't used much for searches (personally, "realty" sounds old school to me). As an agent, "city"homes.com are the most brandable for a residential agent while "city"realestate.com has appeal to both residential and commercial agents as well as being used more in searches than "city"homes.com.
THE MOST IMPORTANT THING thing is to purchase "city"homes.com OR "city"realestate.com domains of what I call "free-standing" cities. ONLY buy the domains if the town/city has a population of 30k or more and is what I call a "free-standing" city. Don't even consider buying the domains of suburbs-agents won't be interested and you'll sit on them. Even if it's a large city that's a suburb of Dallas, KC, or another, don't buy them. If you make smart choices in your purchases and work hard to market the names, you can have success. In most cases, don't spend more than $100-$500 for these domains if you want to have room to make any money.
I've purchased these types of domains for a couple hundred and turned around and signed long-term licensing deals (8-10) years for a total of $2,000. Then, a few years into the license, you can offer to sell the domain to the agent that is licensing it for a couple thousand more for a total profit of $4,000-$5,000. I'm sitting on several domains that I have no doubt I could license with a little work (sending e-mails to agents and there are a few other strategies), but don't have the time to mess with it. Let me know if I can help you with ideas to market them to agents.