We too have just completed the process.  Our experience was a little different.  We went directly to a Gestor (Cardona in Tortosa).  We needed the registration document (or in our case the certificate of permenant export), the original purchase invoice (to avoid paying any import tax) from when we bought the car (it was second hand but we had the invoice) and the letter from the consulate confirming that we lived here.

The consulate letter was obtained by phoning the consulate who then sent us a card to fill in (you can get the card from this site - see 'Registering with the British Consulate' in the 'Useful Info' section from the menu above).  We also needed to send in a letter from our ex-council in the UK to say that we no longer appeared on the electoral register.  We sent the letter from the council and the completed card in and transferred the fee (I think it was 20 or so euros) and they sent us the letter. We didn't need to go to Barcelona at all.

The total cost was €600 - this included everything - Gestors fees, ITV, Engineers report, 1st year road tax and all the Traffic department fees.

The only thing we needed to pay for then was the 2 number plates - €12 each.  You MUST take your document with your new registration number on it to the place you buy your plates from - they cannot make them without.

Nigel