How?

Adding a weekly server that has 100x the rates of this one and only lasts 4 days.
So in those 4 days you got to get stronger and at the end top 3 players will get a prize on the normal server [this one]
So they can level on that server without a level cap so they wont get bored.

A contest that can be hold weekly or daily or whenever you want.
The game gives every one a Pokemon and you have to train it but you can use it only on a specific trainer that is made for the contest . So you can not use it outside of the event. The trainer [NPC] has pokemon that level up the same as yours making it even harder because you will get a normal rate of XP for the Pokemon so leveling will be a pain but worth it.
And of course top 3 gets prize.

After you reach TRAINER level 50.000 you can reborn/prestige so you start from level 1 and the amount of XP you gain will reduce but of course you will BIG rewards for reborn/prestige.
You can reborn/Prestige as much as you want as long you have power to level up to maximum.
Add reborn/prestige points and a shop for it with limited items that change once a week.

Lets say the lvls are around :
lvl 2000-4000 : prestige points 20 + 20% prestige XP
lvl 4001-8000 : prestige points 50 + 40% Prestige XP
lvl 8001-12000 : prestige points 80 + 60% Prestige XP
lvl 12001:16000 : prestige points 110 + 80% Prestige XP
lvl 16001:19999 : prestige points 150 + 90% Prestige XP
lvl 20000 : Prestige points 200 [but took hours grinding from 19.999 to 20.000] + 120% prestige XP

lvl 1 prestige = Exclusive map with more legendary/colored Pokemon.
lvl 2 prestige = Prestige shop with equipment and items all exclusive
lvl 3 prestige = Exclusive gyms 8 new gym badges with prizes.
lvl 4 prestige = Prestige Icon and prestige banner
lvl 5 prestige = Prestige shop 2 with banners and name icons
lvl 6 prestige = Make an own GYM ! [people fighting your gym pay 50 coins but if they manage to defeat you they get a prize you put in yourself]