When levelling the best investment you can get is a full set of new gear every 5-8 levels, cuts down the kill time and increases your survival rate, in other words it increases your money / hr ratio. At higher levels this is less important due to dungeon gear, however again its best to get the cash and go for the big upgrades rather than taking the cheaper incremental options because when geared, money is easy, when not geared, it takes effort to gather.

As a protection paladin you reach the point you can grind the Temple of Karabor and then you have money for free essentially, the same happens to other classes where they reach a gear point where they can farm without requiring a profession easily. The manipulation and saving of money, is almost irrelevant until you reach a gear level you are happy at, and at that point saving for a high level of gear or toys is easy because the non-raid end-game is designed for fresh level 70s through to Kara level basically, being horribly well geared lets you blitz through even instances for cash (a typical botanica run will net 6 Large Prismatic shards and 1-2 Void crystals, Shattered Halls 5 Void Crystals, 1-2 Void Crystals and some primals). The ability to turn gear into cash makes the game economy far more complex than merely saving and suchlike, because its the equivalent to your Ferrari increasing your salary by 20% simply because you can go faster, its a mechanic I dont’ normally hear related to in real world economics.