As you level, you will buy new ranks of spells. If you splurge out on an item upgrade, you will not have enough gold readily available to upgrade to the latest ranks of spells: placing you behind. Moreover, you can buy gear upgrades from the Auction House (AH) or vendors. Furthermore, you may have large investments that need to be paid for professors. You will need to purchase reagents and items such as leather, bolts of cloth, alchemy supplies – unless you have a charitable friend or another high-level alt.
Some class systems from the original game simply don’t have a modern equivalent. The class probably most affected by this is the hunter. The pet happiness and loyalty systems were removed a long time ago, as well as pet training and the ability to use both a ranged weapon and a melee weapon. In these cases, converting the old data to the new system wouldn’t work, simply because there is no new system to match. In this instance, we had to bring back the old code—and we did. Fortunately, the restoration went smoothly, though the reality of having to buy arrows or feed their pets again took a few people in our internal tests by surprise.
I am currently working full time on my Vanilla WoW leveling guides. Soon there will be a 1-60 speed leveling guide for Alliance, along with in-game guide versions available for my members area. As of right now, there is no members area, but if you would like to show support for my efforts into this project, you can simply donate to me via Patreon if you like (you will get some cool rewards in return). Or you can donate directly with PayPal if you like. All donations are highly appreciated and they will only motivate me more to continue making the best vanilla WoW leveling guides on the web.