Well i noted down how many rares you get AFTER you have maxed all N Cards , i only used 250 N Gacha for this test but i got 175 N Wild Cards, 69 Rares and 6 SR Cards, so i guess you could change the 175 N Wild Cards in 17 Rare Wilds , but this will still be not even close to 60 level per day because i saved Pero for 3 Days so count with 30~40 Rare Levels per day, if you are farming at 1-3...

But even if N Cards are maxed you still can randomely receive a level up on a Rare or a SR, although i have to admit in 250 draws i only got this 10~15 Times and not once on a SR from a N Card but it did happen a few weeks ago