4 links start to drop very commonly later on in the campaign. I use the occasional Alchemy Orb, Chrome, Jeweler, Fusing, and blue/magic currencies but nothing beyond this as they are valuable or not worth using this early. I also use Essences as pseudo alchemy orbs. Make sure you have the Neveesink Filter though, otherwise you will be missing out.
GGG keeps things fresh by having new leagues every 3 months which is like a full reset and everyone starts over fresh. There are new mechanics, items and content in the new league and the economy is the liveliest at that point (too lively at some points). Thisis what keeps getting people back leveling your character beyond lvl95 is tedious and not really needed, you can beat everything in the game well before that.
Power creep is definitely a factor though as GGG has to introduce shiny new items for players to chase after. The main power creep has been the rate at which players clear content and acquire money, allowing them to surpass the content faster than before. I dont know about others but for me this was the fastest I killed Uber Elder in a league. And it feels I am getting faster and faster every league and its not jusr my personal skill or knowledge (maybe that is too) getting better but the game having more tools available for players to take advantage of.
That said the most powerful and sought after item in the game is many years old. So old stuff doesn't always lose its value.
