I believe there will be a change in applying for indefinite leave to stay in the UK from 2016 so that minimum income is £35,000. What about maintaining it if I already have it - do I still need to make £35,000? Does that mean even though I've been here nearly 20 years I cannot retire here on an income less than that?
Note that the changes only apply for applications for ILR status:
Applicants will need to meet the Rules in force at the date of application
Once you have obtained the ILR status you are considered settled, and can remain in the country indefinitely, and can usually only lose this status if you commit an offence, or leave the country for more than two years.
However, if your other nationality allows it, and you have the funds for it, it might be advised to naturalize as a British citizen.