honestly it's up to you....
Once you make it to the Master Tier, you will need new clubs... the best for the master tier is the G20 set... The lvl 35 ghost putter is the best putter until the lvl 77 Nike... Cleveland wedges are far superior to the rest... if you use them correctly..
but these are all my opinions, and they fit my game the best...
whatever fits your game at the level you are at...
Wedges and putters aren't about stats, but more about feel... again, whatever you feel the best.
as far as WHEN you should upgrade... trust me, you will know... You will reach a point where you are saying... I really want "___" clubs...
and you will get them.
It's pretty simple really :D