I have had my 2002 LS430 for a while now, so I can only go on what I have experienced, you will get different stories from different folks, but I can only tell you mine.
Q1: Are Lexus's really as reliable as legend has it?
No, the battery on the LS430 isnt big enough for the job, so if you sit in a car park with the radio on for more than half an hour you will need the AA or a mate to come and jump start you, and if you accidently leave an interior light on overnight the battery will be flat in the morning (usually when it is raining), and you cant get a bigger one because it sits in a box which is only the right size for that battery.
Things that are wrong with my car include:
The satnav, which only works when it is warm and looses all of the settings when it isnt.
The automatic wipers, which dont work at all.
And the steering column adjustment, which only goes in and out, and wont work with the memory.
The gearbox is a real dimwit at times and cant decide which gear it wants (but I have found that on all of the Lexus models I have driven).
If you have a pet dog and regularly take it in the car, the alarm system will drive you insane.
Q2: realistically what sort of MPG can I expect, I currently get about 27 mpg. Can I expect much worse?
Depends on how heavy your right foot is, I have seen 2MPG on the readout. I do a lot more town driving than anything else and expect to see a tank average of 18MPG, however when I had a lot of out of town trips last year, I saw better than your 27.
Q3: are there many decent independent Lexus mechanics around? Or do you even need a Lexus specialist for servicing?
Have you got one that services your beemer that you trust? Take the Lexus to him, it still runs on petrol and has four wheels, Its just got two more spark plugs to change when its serviced. If something breaks that the mechanic cant fix then take it to a dealer, and make an appointment with your bank manager to take out a second mortgage.
Even with all the problems I would not swap it (except for an XFR, or an Aston Rapide), because realistically its the best car you can get for the price range, and when you press the loud pedal, it all makes sense.
Dont get one with Dunlop tyres, or change them before the roads get slightly damp,
and dont get a blue one, any other colour, not blue..
I just got blue with Dunlop tyres- why not? what wrong with it?
Yes! you right about color but if to do polish wax and detailing-it should keep dust away.
and what exact tyres you recommend for that car? I dont like Dunlop's already as they not hold even dry road