1. Fair enough. I was simply giving the cost of your deal some context. I assume your deal was for dsg 5dr? If not the manual 5dr is £1k cheaper.
2. Someone who pays £28k upfront won't be paying another £28k 4 years later as they'll have a car worth £13k to trade in. At the end of 8 years they'll have paid out around £43k (or around £46k if bought with a cheap loan) and will own a 4 year old car worth approx £13k. The person doing 2 PCP's will have paid out £40k and won't own anything except the possibility of some equity towards another car.
3. Fair enough. Obviously there are lease deals available on GTi's as well, but i'm sure you probably already know this.
4. I'm not sure how negative equity is irrelevant. If the rear end drops out of the used car market and WBAC offer you less than your GMFV, then the difference is your debt to pay. Also if I were a private buyer i'd be very wary of buying a car that showed up on a HPI check as still having a large amount of finance owing on it. But i'm sure you've thought this through and are happy to take the risk. Agree that leasing is less flexible, but it does give you a bit more certainty in what you'll end up paying out and you can extend for a few extra months if you need to.
S3 is a nice car, completely understand why you'd be wanting one of those.
If you're happy with your deal, then it's your prerogative to go right ahead. But at the very least i'd be asking Drive The Deal or Carwow for a quote for comparison purposes. Or if you just don't trust my opinion, then maybe post your question here and see if any forum members can offer you more help than I can.
http://www.golfgtiforum.co.uk/index.php?board=117.0