There's some very handsome encrustations on those universal joints. Mine usually show some signs of slack well before they get to that point.
On my TD5 the biggest improvement in drivetrain clunk comes from replacing the rear drive flanges. The front ones make a little bit of a difference but the rear ones make the most. Fortunately the flanges tend to wear faster than the halfshafts, which is good because they're a lot cheaper. I tend to favour the aftermarket ones with a screw on cap so you can fill it with oil and get a bit of lubrication on the splines.
While looking at the suspension, it's worth checking for movement on the other joints and bushes. For example, once upon a time I found some movement on one of the bushes where the rear radius arms join the chassis. I don't think it was contributing much to the drivetrain clunk, but overall, the tighter you get your drivetrain and suspension the less of this kind of noise you'll experience.
