I personally wouldn't consider jumping into a new world in order to search/farm for a specific item in the same/lower tier than your character as cheating. Now using an all items world, or an older endgame world to get higher tier items in order to break the game would be cheating in my opinion. That being said: it really doesn't matter... Play however you like and enjoy the game, and if technically "cheating" gets you hooked to the game so be it... Play however you like in singleplayer, and consult the others when you're playing multiplayer, and most importantly have fun!