Question: 2004 A3 diesel vs new A3 petrol 1.4

The lower torque will probably translate into poorer in gear performance. However it isn't bad for a 1.4 petrol. Much more torque than my current 1.6 petrol.
The other number to consider is weight. The new A3 is lighter which helps the power and torque go further.
On paper the COD engine is the closest to a diesel as I've seen in a petrol. However the bottom line is only you can decide if its right for you so get a test drive. Hopefully there are some COD demonstrators about now.

I faced a similar dilemma when ordering my A3 saloon with the added complication that I wanted a S-Tronic and this would not be available to order with the saloon until November. I was not able to test drive a 1.4 COD in June but tried the Golf 1.4 ACT and was very impressed, so much so that I placed an order for the 1.4 COD. There is no doubt that this engine can not match the 150PS diesel in torque or pulling power but I am willing to sacrifice this for the benefits of a lower purchase price, cost of fuel, servicing cost, a quieter and lighter engine. My current Passat has 350nm of torque versus the 1.4 COD's 250Nm but the Passat is 400kgs heavier and the diesel A3 is 65kg heavier. The petrol engine requires a different driving style, changing gear more frequently and holding the gears longer to make the most of the engine's performance. I only do about 8,000 miles pa so think it is not worth the extra for the diesel but time will tell and I will not rule out a return to diesel if I miss the torque or the fuel economy of the 1.4 COD turns out to be a disappointment. As you say it is difficult to judge on a short test drive, I only drove the Golf 1.4 ACT for about an hour but on a mixture of roads. Maybe worth trying to get a demo for a day or the weekend before committing.

I think it is perfectly reasonable to expect to get a demo car for a day and there is certainly no harm in asking. I had a Passat to try for a day before buying my current car although it was a 2.0 petrol as the 2.0 diesel 168bhp was not available to demo when I was ordering. My previous car to that was a petrol A4 Quattro and again I had a demo of one for a day. Your problem maybe getting a dealer who has a 1.4 COD and then if there is a demand for people wanting to demo it, if they let you have it all day. As you say the fuel economy of the petrol is not so relevant if you only cover a small mileage. I think the time you would miss the torque of the diesel most is if you were loaded up with passengers or going up a steep hill (or both) when you might need to work the gears more in the petrol.