We live in Miami, have a '99 RX300 w/66K miles. My understanding is that you do not 'tune up' the RX300: a computer chip maintains/adjusts settings, and if there is too much roughness or other problem, it means some kind of repair is needed (in addition to the regular factory-recommended maintenance that I assume you complete). I do not know of a mechanic other than Lexus of Kendall, where the foreman (Carlos) is friendly and knowledgeable. Re: cleaning... - ther are other posts in this forum which detail how to go about this.
Let me know when you find the ideal: a great, honest, inexpensive, knowledgeable mechanic!
Best of luck
pauljcl