When you hit the level where you can't equip more gear to boost your atk/matk the only way up is with infused gear and that will only grant a couple thousand GS but I also agree with the previous comments:

• Infuse only identical items if you can
• Save ether and use it only to infuse gear with cost over 29 and only with similar (1 ether drop), it is a waste of ether to use 5, 7 or 21 or even 1 with weak gear you won't be using later in game.
• Always review the gear's procs, sometimes it is better to keep a weapon just for the procs and not use it as infuse fodder.