My 03 SPI is at 155,000 miles and going strong
I really baby it while the engine is cold, and use 2 oz. Lucas upper cylinder lubricant at each fill up. The UCL seems to give me an additional 1 MPG, but may also help keep the valves clean. May need some luck to get to 200,000 miles with out the inevitable valve seat drop.
I will be taking my chances for now, but will consider pulling the head and bringing it to a shop for the usual service (hardened seats, etc.)