World of Warcraft: Burning Crusade launched on June 1. The pre-expansion patch on May 18 began the transition to Burning Crusade Classic. When you log in after that patch is deployed, all players will have to choose whether to continue on into the Burning Crusade or transfer to a special set of servers that will stay locked in vanilla-era WoW where the level cap is still 60. Every WoW pre patch event is a pretty big deal but the one for TBC Classic is particularly important. A lot of veteran World of Warcraft players first stepped foot into Azeroth (and Outland) during the lifecycle of the original Burning Crusade expansion. Now, many of the same players are returning to once again experience the opening of the Dark Portal. Of course, this time around it's during the WoW Classic TBC pre patch event, which launched just recently.
The reason you should invest your WoW Classic TBC Gold now is that almost everything will get more expensive after TBC Classic is released, and even before that. Investing your gold now is the smartest thing to do, simply because of the gold inflation that comes with every expansion.
Professions are key if you want to farm WoW Classic TBC Gold at a consistent rate. There are plenty of materials from Classic that have become valuable in the TBC pre patch due to the new level boost service implemented by Blizzard. This service only boosts your level but you still have to train professionals from scratch. In addition, there are also lots of people playing Draenei or Blood Elf who are scrambling to max out their characters and professions before the expansion launches.
Golden Sansam is sort of like the Alchemy equivalent of Illusion Dust. Golden Sansam is not used for a lot at the moment, even though it is quite a high level herb, making it quite cheap to acquire. Golden Sansam is used in some of the first potions that Alchemists can make in TBC, so it will be quite a good investment. But the prices are expected to increase substantially into TBC as players realize that the best way to level up certain professions past 300 is to use some of these old crafting reagents.
Speaking of Blood Elf Paladins, there's currently a lot of demand on the Horde side for Librams of Fervor. These items can drop from many mobs and bosses but always on a very low drop chance, so they're not easily acquirable. But they are very valuable throughout TBC since Librams, in general, are pretty rare. Luckily, prices for Librams of Fervor on both EU and NA seem to be fluctuating a lot at the moment. You might be able to buy one relatively cheaply if you're patient and then flip it when the prices inevitably go up as more and more Horde Paladins reach the max level.