tonearm upgrade, how far up the food chain?

I currently use a Rega RB 300 upgraded with the Origin Live structural mod (i.e. counterweight) and Incognito rewire. It's on a Thorens TD-850, Grado Statement Reference cartridge. Based on comments here on the Gon, many seem to feel that upgrading the arm should come before the cartridge or table, under the circumstances. How far up the ladder do I have to climb to get a noticeable improvement? And, do arms (that is, their bearings) really wear out, or their performance decline, with normal use? considering midlevel Origin Live arms, given the Rega mount. thanks in advance for suggestions.