I recently had a handling package fitted so hopefully I can provide some insight from experience into which compromises need and need not be made.
I have a Rhoddy Harvey Bailey bespoke GTA damper pack matched with Eibach Pro Kit 2.4 springs on my 1.9 JTD Sport. It's not a bad match up for B road blasts actually, the car looks great and eats up roads, potholes the lot at full pelt, but... and this is a fairly large but... the sump absolutely HATES speed bumps. It is admittedly less crashy than the standard dampers and Sportpack springs, while also sitting 10mm lower at the front and 30mm lower at the rear so kudos where due. I'm not quite 30 yet so I went into this with my eyes open. Sometimes though, I wonder if I should have kept the Sportpack springs on... until I find a quiet road that is...
The consensus is that the main problem with the handling isn't the springs but the dampers. The problem is outlined in this article posted in Auto Italia:
Monza Sport were selling the aforementioned GTA/JTD handling pack for around £400 plus VAT last time I looked. The Bilstein B8's have been breathed on by Rhoddy Harvey Bailey, a man who knows his stuff about bound/rebound settings (apparently Alfa don't). They are ideal for your GTA because they are bespoke items matched to your car's spring rates. I wouldn't recommend lowering the GTA since it looks balanced and is plenty low at standard ride height. Instead consider an Eibach ARB from somewhere like alfisti.net, this will have a similar effect on reducing body roll. Beyond that, perhaps fit a Quaife differential, anything else falls foul of the law of diminishing returns at around this stage.
You might want to consider then fitting the ARBs from the GTA on your Sportwagon, or at least the rear one to reduce understeer. Again, replacing the dampers will suffice but for a daily driver, I would Perhaps opt for Bilsten B6 since they are between the B4 standard and the B8 designed for lower harder springs. I would have recommended the Sportpack springs which I had on my saloon (I have a set which have done 40k miles hanging around incidentally
) However, I'm not sure if they did them on the Sportwagon or if 1.9 springs would even be okay on a 2.4. Anyway, I'm sure someone else can recommend a suitable spring. Think I'll +1 the apprehension to fit GTA saloon kit to a diesel sportwagon. In sum, I wouldn't go lower than the sport pack ride height, buy an aluminium sump guard, and be prepared for the Eibachs to be harder than the GTA if you go that way...
Hope this helps,