I have had similar ride deterioration with my 2000 SE, which has 15X7 Borbet Type E rims with H rated tires (Kelly Chargers). The harshness is rattling the dash almost constantly. It's almost as if the car is riding on round rocks. I'm so glad to have softer Dunlop Graspics on for the winter. It's only got 60M on the odometer, and has been treated well except for the rough concrete around Seattle.
I don't know if the BAT suspension will help, put it's on my Spring '06 potential buy list, as on the other end of the scale a set of Monroe SensaTracs with stock springs if my need for comfort surfaces.
It sounds like in any event, you have got your use out of the stock shocks. Good luck with what you do. Would be interested in knowing how the BAT suspension works in daily riding if you go that way.
Happy trails.
