IIM

Well, CV doesn't have points, it always carries weight. How strong your CV is and how capable you are. The most important thing which will be considered during your placements is your CGPA. Companies will shortlist mostly on the basis of CGPA. There have been times when the list of shortlisted candidates for some of the best firms consisted top 10-20 rank holders of the college (literally). So, no matter what anyone says, CGPA shouldn't be neglected. Especially for high demand jobs like investment banking, CGPA is a deciding factor.
After CGPA, they will check for relevant internships. So, make sure that you do at least one or two internships in relevant fields in good companies so that you don't look like a novice. Then they see the past academic records and awards and honours including scholarships and fellowships.
So, the order of importance would be:
1. CGPA
2. Relevant internships in reputed companies
3. Awards and Honors
Don't think that extra-curricular activities matter a lot. It is good to have some to show that you are an interesting person. It may have a bit importance in marketing but not at all in finance. Having important position of responsibilities like the president of the student council or something may be helpful.
But don't neglect academics for that.

The IIM tag promises the average Indian kid a better life. There is enough proof in the newspapers with reports of the sky-high salaries during the annual placement seasons at these top-level institutes.
I believe that almost anything can be learned off the internet. But the benefit of an education in an IIM is the exposure that they provide. Those from institutes other than the IIMs also make it big and have humongous salary packages. To get into IIMs one has to crack the prestigious CAT. CAT is the exam for smart people, so if you are from IIM, it means you have cracked it. That leaves an effect on the minds unknowingly. People are biased about IIM. So it affects the CV of the students. Having a degree from a top business school increases your chance of landing that job. It is not very much prominent but it is a factor.

Until a decade before, IIMs were the most desired B-schools. In 2009, things started to change with the opening of several new IIMs, starting with IIM-Rohtak, and followed by more, in Ranchi, Raipur, Trichy, Kashipur, Udaipur, Nagpur and six other cities. While this means that the aspirants have an elevated chance of getting admission, the value of brand IIM has been eroded in the method. The new IIMs have not been able to match the standards of the older ones on various parameters, including the quality of faculty/students, infrastructure, as well as ability to attract top recruiters.
Apart from quality education and research work of students and faculty, the older IIMs had been valued chiefly for the high-paying jobs their students got. This led to high expectations from the newer IIMs too. The reality has turned out to be contrary.
The newest IIM Jammu, IIM Bodh Gaya and a few others still have to get a campus. Though faculty shortage is affecting nearly every B-school, the situation is worse in the new IIMs, partly due to their geographical location.
So I think the government should focus on developing the older ones instead of opening new IIMs.

IIMs and IITs are really focused colleges and can't be compared to the US and European universities. Those universities house various departments which all come together to enrich the student experience. And, additionally due to the smaller size of the universities in India, they have low number of foreign students and faculty. Also, the research output is lesser than universities worldwide due to the focus on placements. But, in general the kind of students that enter and the faculty that teach are the smartest and most hardworking in the world. Also, both the institutions have good penetration in the network, and the students and research benefits from it.
The ranks are for the one year MBA program of IIMs, and don't represent the quality of their flagship PGP Course. Hence, I would say these rankings are not a good metric of assessing/comparing the quality of IIMs against other institutions.

There are a lot of good private colleges which make it to the top brand of B-Schools. The below-mentioned colleges are at the top because of their living experience, placement performance, Selection process, future orientation, alumni networks, brand value, curriculum and quality of education.
1. MDI Gurgaon,
2. SP Jain Mumbai,
3. Narsee Monje Institute of Management Studies Mumbai,
4. Faculty of Management Studies, New Delhi,
5. Indian Institute of Foreign Trade New Delhi,
6. ISB Hyderabad,
7. IMI New Delhi,
8. IMT Ghaziabad,
9. National Institute of Industrial Engineering Mumbai,
10. Jamnalal Bajaj Institute of Management Studies,
11. Symbiosis,
12. Great Lakes,
13. BIMTECH,
14. Goa Institute of Management,
15. Indian Institute o technology Kharagpur,
16. Indian Institute o technology Mumbai,
17. IRMA,
18. TAPMI.
Students can get into these premier institutes by cracking various MBA entrance exams.

We can't say IIM-Ahmedabad is charging very much, but among the IIMs it is on a bit higher side. The facilities provided at IIM-A are really good as compared to any other college. IIM-A has world-class infrastructure in terms of classrooms, dormitories, computer centre, library and sports facilities. The world-class infrastructure created on the institute's hundred-acre campus provides an ambience conducive to stimulating learning. The architecture, classrooms, library, research centres and computing facilities all combine to provide a holistic learning environment.
A state-of-the-art computer network with more than 2000 nodes connects all the members of the institute's community with each other. This network has a fibre optics backbone with one or more fibre segments reaching every building at the campus.
A good library, all sports facilities, and good campus life is what IIM-A offers.

As per my experience I don't think that an year gap affects for CAT preparation adversely affects your chances of getting admission in any institute in IIMs or any other institute of India. The entire interview process is meant to gauge the students on their knowledge, skills and attitudes as well as their inclination of doing a MBA program.
If you are dropping out of your current job for one year there should be a justification as to what were the reason for opting out of your job. There are various examples of students who have scored a hundred percentile while working and thus the interviewers always discuss the reasons for dropping out. But, if you are able to justify it well and convince them about yourself. I personally don't think that it would negatively affect your chances into IIMs or any other institute of India.