There's nothing in Maplestory that you can't buy with the ingame currency aside from cosmetic items
shielding wards
miracle cubes
gachapon tickets (to get rare items)
pets, and pet equips that add attack
scroll percentage boosters
shops
scissors of karma (to trade rare items)
2x exp/drop
item locks
those hourglasses that extend item times (can be used on certain non CS items)
mastery books for DB/Evan
teleport rocks
inventory slots
aura rings (CS item. gives stats)
second pendant slot
wedding coupons (rings give stats)
vicious hammer (more slots on an item = more upgrades = more power)
access to the MTS (buying hacked weapons) <--- this one makes you a friend but it's still buying power
all of these give some sort of advantage that cannot be obtained A) easily or B)
at all in regular non-paid play
the list goes on, and on, and on.