Good question!
Most Gringos aren't worried about becoming citizens, but they do want to get legal residency.
- As a resident you don't have to leave every 90 days to renew your tourist visa
- You don't have to worry about being denied entry when you do come back (extremely rare, but could happen)
- Some places, as you mention do have special prices for residents not available expats on their tourist visa.
Immigration varies as to their treatment of "perpetual tourists". For many years there was no need to get residency, even though getting it was relatively easy.
For a few years there was a crack down on Europeans and North Americans staying past their 90 days repeatedly.
Currently there is not as much restriction on that, but the bureaucratic hoops for getting your residency have gotten tighter, so the process is more arduous than in the past.
There aren't any tax advantages (on USA taxes) to living overseas legally versus illegally. Although legal residents could work and would therefore be eligible for the $80,000 foreign earned income exclusion. As would people who qualify for the inversionista program and work in their own business.
If you were to renounce your US citizenship and become Costa Rican, which you can do after 2 or 7 years under certain types of residency, then you would no longer be liable for US taxes. (Although if the IRS can say that you are changing your citizenship to avoid taxes they can make you liable for 10 additional years).
