With how easy it is to get to level 62 these days, marni stones really make no sense below level 63. But above lvl 63 they give such a miniscule amount of exp there is no point using it. 

My suggestion: redo Marni stones for lvl 63+: make them more expensive and make them give exp% that is noticable for levels above 63. 

Advantage: faster levelling above 63 and a silversink people would be interested in. 

agree with this one

I love this idea! I'd like to expand on it slightly and say that a great option would be to make the cost of them a variable based on your current character's level as well as their reward for completion. Doing this, they would need to be character bound however in order to avoid minor exploits. 

or remove them.