As it would still be active income, not passive, I'm not sure that an LLC would be useful in obtaining a rentista visa although I personally have no experience.
If you have the disposable income, you could probably deposit a lump sum in a trust and as long as it satisfies the monthly income requirements, that might be a solution.
With regards to citizenship, well, that is really a personal question. For me personally, that is not a decision that should be undertaken lightly as citizenship is a binding commitment and entail moral, legal and financial responsibilities. For me, that certainly isn't a decision you undertake to deal with a visa situation. Others may feel differently.
PS - I don't believe you can obtain citizenship, renounce it and then get residency after the fact. If you have other information, I would be very interested to read it.