We had to take Sanskrit because that was the only teacher our small school had. I forgot most of it in a couple of years. Modern Sanskrit taught in schools doesn't even enable you to read religious texts because the Sanskrit there is totally different, so I just don't see the point of it. I know in the west too some students can choose to learn Latin as a foreign language and some indeed do, but at least in their case it is a choice.
I think the most useful thing we could do for nation building is make North Indians learn a South Indian language and vice versa. At least it will have some utility in terms of cultural exchange and nation unity and temper regionalism.