Since there are medals for intermediate rewards in the collector line (30/80/150/250/400), I'd like to see the same added for the quest medals. Reaching intermediate goals could give a nice push to motivation. Since the quest specialist gives 5 all stats, 150 hp/mp and 10 avoid/jump, an implementation could be a 1-all stat, 30hp/mp and 2 avoid/jump at 250 quests, 3 all stats, 75 hp/mp and 5 avoid/jump at 500. Other options would be lower intervals like 200/400 but since the time spend completing more quests really increases when you've already done the easy ones I'd say 250/500 are decent breakpoints, maybe even 300/600 would be fine.
Are you looking for intermediate medal rewards for the stats or just to increase the amount of medal collected overall? If it's just stats, there are other medals that already covers them, so quest medal is an direct upgrade. Easiest example would be 1 all stat lv 70 medal (1 all stat 180hp/mp maple explorer and 1 all stat 150hp/mp ossyria explorer) 2 all stat lv 120 medal (anni medals) 3 all stat christmas medal and ellin medal. With collectors, there isn't any replacement for medal with attack stats other than lv 200 medal iirc.
Not for either necessarily, I mostly think it just makes sense to have intermediate rewards for quest amounts because first one at 800 is just very late. For collectors there are also the 30 and 80 sets ones which dont have any attack but just hp.