One of the main sites that garner visits to our mini city, and keeps it balanced, has an option to works with multiple IP adresses.
The more cities you can give multiple 'visits' to the higher up the ranking you, as a member, move. The way the visits are made not all the members choose to spend the time visiting all the other cities so those members at the top of the rankings are more likely to collect more visits for the cities they represent. As a rule it takes me around 1 minute to visit 1500 other cities with my single IP but in return Cable Forum City is visited on average about 4000 times a day by other members many with multiple IPs including one member who has used 2295 different IPs so far to-day
http://utopia.lv/exchange/?do=links .. .I am not sure how much of the site can be seen without joining but so far, 2/3 years, I have never had any spam or problem if you want to try it out.