Maybe if your electricity is free or cheap mining is still worth, but if your electricity cost is expensive is not worth. Remember, a lot of peoples mining and it makes coins difficultly increased and the market condition is not supported now.
You are right. The mining market is very mature now, there are plenty of companies running their mining farms all over the world. The key factors are electricty price and calculate power(equipment).
Mostly companies are GPU distributor and then they resell their cards for higher price. They earn from mining and earn from distributing the cards..
That's why the difficulty is getting more increases and the price of cards is getting increase because they are holding gpu while mining then they resell them in higher price..
As of now i still getting profit but it takes year before a can break my ROI so before i break the roi i think selling them would be the best choice because i think nvidia or AMD will release a new graphics card with higher performance than to old cards.