Quest reward experience is increased by a similar amount.
Basically a sweaty speed leveler could aim for sub 5 days /played in og vanilla, in tbc you can aim for 3 days /played.
As for prep, there’s a ton of things you can do now to make the journey easier… Buy yourself some weapons, toss fiery enchant on them for a start… Maybe snag some cheap armor as well are probably the biggest things you can do to speed things along relatively cheaply. If you really want to get sweaty, there’s tons of other enchants, buff elixers, health /mana potions, explosives, etc you can also farm up that will aid the journey.
Skinning knives with Fiery and spell power. Also snipe cheap twink items for good power boosts while leveling. Summoners to get you out of the dranei starting zone are also good to set up if you have access to them.
Either prep a blacksmithing kit or a tailoring kit and potentially a LW kit aswell.
Aside from that people forget that the draenei starting zone has amazing leveling gear and that helps a metric truckload on those first problematic levels.
I think the 1000000000000000 people there are going to outweigh any possible benefit for level-up gear, layering or not. If the devs slap a super-quick dynamic respawn on the entirety of the 1-20 area and bump up drop rates of every single quest item and make all the key npcs open-tag, it MIGHT help.