A massive difference.
In terms of the handling on my car, only two mods I've done have noticeably improved things - the first was changing the rear beam bushes to polybushes, which made the rear feel much more planted and solid. It's worth mentioning my old bushes were really bad and made the rear end feel like it was totally disconnected from the car, so keep that in mind. The other thing was the rear ARB. Every time I take the car out on a b-road or anything remotely twisty, I'm feathering the throttle to try and get it to step out, and it just stays planted. I don't even have especially good tyres on there - just Bridgestone Turanzas - but I'm yet to find the point where they lose traction, and believe me, I'm trying.
My feelings now that I've had some time to think about it is that on the
mk1 Leon, the front is actually pretty good, but it's the rear end that needs attention. Being a front wheel drive car, it's at an obvious disadvantage, but the rear ARB does a really good job of cancelling most of that out. It's much more confidence-inspiring with the ARB especially, and I enjoy driving the car so much more now.
If I were to do anything else, I'd probably lower it a sensible amount, just to bring the centre of gravity down a bit. My only concern there would be scraping the sump as on my TDI it's already quite low. It's a shame I just replaced my shocks because I could have done that then, but I didn't have the money to do that, as is always the way.