I agree entirely. I also have a new 140 common-rail at the moment. My previous A3 was a 170 PD and I had a 140PD before that. The new engine is so much better, much quieter and more refined. Before I decided on the 140 I test drove both the 140 and the 170. The 140 is more economical and I wanted to see if I noticed any real difference between the two. The answer is Yes I did, but not in the way you might think. Both cars and my previous 170 and my 140 before that had s-tronic gearboxes and the new 170 cr was slightly noisier than the 140 and I also found I needed to change down to a lower gear for some corners and roundabouts. I was told by an Audi Master Technician that this was probably because the 170 has a slightly bigger turbo than the 140. Performance wise I never noticed any difference in normal day-to-day driving. I decided to go for the 140 and have never regretted my decision.
I recently took my A3 to Germany and Austria for a holiday covering some 3000 miles with all sorts of driving. The car was quite happy cruising at 120mph for quite long periods on the German Autobahns but was equally happy at much slower speeds in Austria and on mountain passes. My overall mpg for the whole holiday was around 47-48mpg. This is some 5mpg better than a similar holiday a couple of years ago with my 170PD.
If you do not the extra kudos of owning a 170, certainly with the new common-rail versions, I would say go for the 140.