Why should you ever stop promoting? Isnt possible traffic limitless or are you just thinking in terms of search engines?
Of course there's not a answer, you can promote consistently, and alwayis increase your traffic, there's not a limit. If it was true, it would never exists big sites.
I need to know the tool which really shows number of visitors per day? Google does not show other visitors.
I'm getting around 20k a month, but I will tell you, it all depends on your conversion and return on investment. I've seen sites that get 1,000 a week that make couple grand a month, and sites that get 10k and barely make $100 a week.
I started two sites about a month ago. One is already getting about 300 unique visitors a day, while the other one is only getting about 100 a day. I check the stats each day, and the "worth" of the two sites is what I am paying attention to. I enjoy putting them together, but eventually I will sell them, and that is where my money will come from. If your site is making you enough of a profit, then there is no reason to not start another one, and just keep an eye on the first one to make sure the money keeps coming in. I don't know if the count of the visitors is really the issue, especially if they start to fade away. Good luck!