Assuming people are actually willing to purchase 5 extra entries per day (300NX each/$1.50 per day, or up to 20 passes per month from Rewards Shop) this quest still takes 77 weeks to complete. That's 539 days, or one year, six months and one week. In terms of NX purchases, that's $808.50. For a medal that gives Lv. 100, STR/DEX/INT/LUK: +7, Weapon ATT/Magic ATT: +7.
Now let's assume what most people will be doing and just taking the 2 free entries per day and that quest skyrockets to 1080 days, which is almost three full years. And remember, Monster Park can only be done up to 7 times a day per account meaning that you're only going to realistically claim the medals on just one character, every 539 - 1080 days, assuming you don't miss any days.
Now, let's remember the totally free content that only takes about 4 hours to complete and you can start at level 33: Masteria Through Time. Completing this gives you a Lv 33 medal with +15 all stats, +500 HP/MP, +8 attack/magic.
How about setting more realistic goals for this Monster Park quest, at just 7 entries per day. Or double. Triple, maximum.
Also please correct me if my math is wrong on how long/much money it takes to complete the Monster Park quests.
Edit: Slight correction. The final reward gives a badge, not a medal, but the Ghost Hunter Badge is still tons better and easier to obtain. Even the Crystal Ventus Badge is better in comparison thanks to the boss accessory set effect.