Excellent feedback by everyone.
Just my two cents:
1. The corolla shape from 2015 onwards was same for GLI, altis 1.6 and altis 1.8. Due to engine to body ratio, altis 1.6 and 1.8 versions had better fuel economy than the GLI one. My mindset might be desi but i believe the body weight was well taken care of by the stronger engines hence the better fuel economy. Saying this as a user of the cars.
2. Similary in Suzuki cultus and suzuki wagon R. Both cars had the same K10b engine yet the body weights were different with cultus being lighter. Cultus mileage was always better than that of wagon R. Saying this as a user of the cars.
When i had the option of 1.3 and 1.5 ativ versions, i went for the 1.5 one because of many factors including the better mileage you get from a bigger engine. A bigger engine would use lesser power to bring the car to said momentum from a state of inertia rather than a smaller engine. I think its simple physics.
Due to cvt transmission the fuel consumption is also managed properly.
At the end i would always ask a potential buyer to look at his or her pocket.
Main difference between a 1.3 ativ x and a 1.5 ativ x versions are below:
Features 1.5 atix x cvt has:
1. Digital climate control (helped me alot in winters without any shadow of doubt)
2. Drls (can be installed after market)
3. Reverse camera (can be installed after market but the quality of factory fitted one is good.)
4. The sound system(its good but it could be better if you have a pioneer or kenwood one installed after market. In total there are 4 speakers and 2 tweeters. One thing....bluetooth connectivity and voice calls are great in the factory fitted system).
5. Bigger and better engine.
6. Eco mode and sports mode. (I have found eco mode useful when i want to drive at lower speeds without engine compression and i have used sports mode to get out irritating slow traffic or for over takes.)
7. Acoustic noise control front wind screen. This feature was provided in grande only and now in yaris 1.5 ativ x.
8. The steering controls on 1.5 ativ x are even more than the ones given in grande 1.8. Call pick and end. Volume up and down. Mode. These are on the left side.
Right side has the imid contols.
9. The imid is great. The speedometer is worth it. Has the same as the latest Toyota axio. I would recommend 1.5 ativ x because of it as well as it provides utility in the driving experience.
10. Push start and smart entry. The latter is useful.
11. Chrome door handles. Looks good only on silver coloured car IMO
Features common in both 1.3 ativ x and 1.5 ativ x:
1. Same rims and tyres
2. Fog lamps are factory fitted
I dont know if there are any other similarities.
At the end it boils down to two reasons; ones pockets and their preference. I dont believe in after market accessories due to warranty issue hence i went with the fully loaded one. If one is already ready for after market stuff and warranty issues arnt a big problem and they can survive without the 1.5 ativ x extra features then 1.3 ativ x is a good buy.
You will get a mileage of 12 to 13 with AC within city if you drive with a light foot from the 1.3 version. Because my 1.5 is giving me 14 to 15 with a normal to light foot with AC on all the time within city.
Dont believe the mileage given in the imid. As per it my cars mileage on average is 18km/l 
