Its a GTV trait.
Heavy front engine with too much weight over the front wheels = tough job for any suspension setup. Ive had two GTV's one completely standard (cant understand why people rate the handling so well like this) and my current one with bilsteins shocks and eibach springs (and Q2 diff).
Yes the current car is alot more positive to drive, alot quicker and with more traction (thanks Q2!) but it seems there is no solution to this cars poor ride. My mechanic (who races his 3.0) thinks best poor road solution is bilstein or koni's all round on standard springs. I think i am going to remove the eibachs soon.
But here's the funny thing. I was asked recently to 2 bags of chicken feed for our little cluckers, each weighing 20kg. Adding 40kg to the boot of the car made a notable difference to the chassis balance AND also slightly improved the ride, i really enjoyed the drive home!! I also notice that when i have a passenger in the front the car seems to settle down abit and ride a little better. I think you should try and get 40kg of ballast in the boot and stick some heavy things in the rear seat footwells and to play around with weight distribution of the car as i think it really made a difference!
It sounds stupid i know and i await the bashing from other GTV owners!