Yeah, i had an a Leon Cupra for a while. I've only given the LCR a test drive for 30mins or so and i've never driven an S3. There is loads of info on them on seatcupra.net.
My general observations on the Leon compared to the A3:
Leon interior is noticeably 'cheaper' in terms of material and build quality, but it looks exactly the same. The 225LCR does have a very nice steering wheel though
LCR has bags of power but i find the traction control intrusive, easy enough to switch it off though.
Stock handling is actually fairly poor. This is, in part, due to the pony tyres SEAT spec for it. I've been told that a simple swap to GSD3's etc transform it but even then if you want to exploit all the power you'll need to change the shocks, springs, rollbars etc. It's basically the same chassis as a A3 1.8T Sport so no suprises there.
The LCR Brembos are great.
The LCR looks great, but still doesn't beat an Audi badge (IMO).
If i had an S3 i wouldn't sell it to buy an LCR. Pablo, i'm not sure why you think it'd be more practical? The only thing you'd be saving money on is the Haldex servicing. It's still the same economy, tax, insurance, and basic servicing (if you use an independant specialist). The residuals of the LCR will be worse than the S3 so i've no idea where you'd save money.
Haven't you only had the S3 for 5 mins? I guess you've done the same as me and blown wayyyyyyy too much cash on modifying it?