1. IMHO the choice only needs to be made on the DZire, since the i20 N-Line only has the iMT option. If you are not an enthusiast, then you should stick to the most convenient drive-train and the automatics are better. However, the iMT is not as convenient as full automatic, since you will still need to do some work.
2. You should not split hairs over resale value. These are old uncle myths. There are many things which determine resale value, and if you buy the Dzire, you are buying an old platform with an old engine, there will be plenty of options in the second hand market. You can check with orange-book-values on second hand sites.
3. The i20 N-Line has a turbo petrol engine for enthusiasts. It will not give you pretty fuel efficiency numbers. I own the same engine with a DCT.
Also word of (unsolicited) advice. I think you are looking at a practical car purchase, you are looking at the wrong models, and comparisons.
The Dzire is an old car, the i20 N-line is an enthusiasts car and is very expensive.
I would strongly recommend you look at other options that are better value and serve your needs. For eg, the regular i20, and maybe other cars that compare, like the Baleno or even a Ciaz which are in that range and from the same stables.