IMO, that price is too high. I get that the mileage is low and it's almost a 2006 reg, but still seems expensive to me.
I take it you know the car's owner and it's history. Does it have SATNAV and Mark Levinson Audio? These affect the market value.
Is it madness? Personally no. I bought my Lexus IS earlier this year. For the price I paid, I could have bought a far newer reg car from Ford, Renault, Skoda, etc, or a similar age car from BMW, Merc or Audi. My choice was Lexus, because I liked the look and how it felt to drive it, along with their reputation for reliability and the brand kudos.
It will cost a bit more to run than your fiesta, tyres, tax, fuel etc.