[orib]

If you can determine an upper bound on n, then your algorithm is technically O(1), and you don't have to worry about scaling.

If you want to be able to handle any value of n, and expect it to be large, you should care about O(n^2) algorithms. You don't have to necessarily get rid of them all at once, but you should at least know where they exist and have them listed as possible pain points or places to start optimizing.