I like to have the ferris wheel in my parks but eventually everyone stops going on it.
Even if I make the price free I only get about 3 peeps on it... How can I make the ferris wheel more attractive to my visitors?
This is actually a complicated subject

. But I'll give you the short version here.
Price has nothing to do with this. What attracts peeps to rides primarily is the ride's prestige. The higher this is, the more peeps it will attract. Price only comes into play once the peep actually gets to the ride and discovers it costs more than he has left in his pocket. But before that happens, the peep has already decided, based mostly on prestige, to go on that ride. So, to get peeps on a ride, you need to up its prestige relative to other rides.
Prestige is a combination of several factors:
* The ride's excitement rating
* The ride's duration
* The ride's scenery
* The ride's age if you have that turned on. Prestige falls as the ride gets old until it becomes "classic" at which point it goes up again.
Flat rides in general are disadvantaged compared to coasters because they only get queue scenery, not track scenery as well (NOTE: I haven't yet tested if adding triggers to flat rides helps here). Assuming all rides in the park are equally pimped to have 100% queue scenery, that's a wash anyway. Tame flat rides are further disadvantaged because it's impossible to make them exciting. So, the only way to up the prestige of a tame flat ride is to increase its duration by adding more sequences. But the longer the duration, the lower the throughput, so there's a practical limit to how long you can make the ride last.
HOWEVER, the weight peeps give to prestige seems to be a stepped function instead of linear. These steps appear to happen about every 600 prestige points. IOW, all rides with 0-599 prestige are considered about equally attractive, and then 600-1199, then 1200+. But a ride with 620 prestige is WAY more attractive than a ride with 580 prestige.
So, for tame flat rides, if you can get the prestige somewhat above 600, it should compete fairly well with most of the rest of the park. Its stats will still be tame so it won't get a whole lot of business compared to more exciting rides, but it should at least stay busy enough not to be a total waste of space.