I think Megan Racing also makes a header for the F23A4 IIRC. Have you cleaned your intake recently or at all? I saw a photo of one the other day that was removed and cleaned, and holy scheiß was it dirty.
Not sure about the flex pipes. My 98 has 220k miles and the flex pipe is still good. A little dented from being lowered but still good. My 95 Camry had the flex pipe break but I still drove it and sold it. The flex pipe only broke because the motor mounts were shot and caused excessive movement and vibration that over stressed the flex pipe. I used to run that thing hard. It lived at 6k rpm every day for years.