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.
I would go table, arm and cartridge in descending order of importance. The relative place of arm and table can be debated but both will have more influence than the cartridge in that there is no way that the best cartridge can perform with inferior table and arm. The 300 is quite a good arm, make sure that it not a sideways move. You don't mention your phono stage, you might get more improvement for your money here depending on what you have now.
I think you should use this formula or close to it:
50% of budget to your table
25% for your arm
25% for your cartridge.
it looks like I am already in the ballpark of the percentages referenced by Nickt. Phono stage is an AR PH3-SE modified by GNSC, which is not bad. Upgraded from an EAR 834P, which was a tremendous improvement.
try that really cool Terminator tangential arm, I want to know what it sounds like but I am afraid to try it first. It looks so cool.
To answer your last question, arms do not wear out with normal use with two notable exceptions. Arms without sealed bearings, when used in an environment with airborne pollutants, such as cigarette smoke and excessive dust can have problems. Secondly, incorrect mounting of the cartridge can cause tortional forces on captured bearings that result in Brinelling (flat spotting) of the bearings, which is why I suggest mounting cartridges with the arm off of the turntable.

I would also agree that the turntable is the engine of sound, as it were, but it can't wear a record. A sticking bearing, poorly polished, or misaligned stylus can. Just some food for thought. I won't get into the audiophile side of things.
Dear Lloydc: IMHO you have a " so so " tonearm and a " so so " phono stage when you have a top rated Grado cartridge that is a great performer and a one that deserve the very best you can get on tonearm/phono stage if you want that the cartridge show you how good is in reality and that today IMHO it can't do it even if you change the TT.

The cartridge/tonearm IMHO is one product not two independent products, a cartridge must be mounted with a matching tonearm not with any tonearm but with the best match for it.
In the other side the phono stage is very critical link in the analog audio chain because is inside this " box " where the cartridge signal must pass to be processed not only to increment its output but to mate the inverse RIAA eq ncesary for a even frequency response, is in this phono stage where the cartridge signal " suffer " in true and where that signal is degraded maybe the most.

The Thorens 850 is a very " decent " TT and for the moment could makes a very good job.

Try to find a removable headshhel tonearm design and a phono stage that can handle ( with out setp up transformers. ) the 0.5mv of your Grado.

Regards and enjoy the music,
Regarding the Rega 300 I agree with Stanwal and disagree,
logicaly, with Raul (sorry Raul). I.e. the 'so-so' qualification applys for the original wiring but the Rega is easy to rewire. I bought this tonearm for my son and deed riwiring myself. BTW my son is also reading this forum
so such 'so-so' qualification my 'disturb' our relation.
Agree with Raul, he hit the nail on the head.

Aiming for some cost ratio is largely pointless, since the performance and compatibility of components cannot be judged just from their cost. OTOH, good lessons can be learned by looking at the ratios of systems that work vs. systems that don't. In that vein, here's my system with either of two carts:

Phono stage...........8
Cart 1 (LOMC).....4
Cart 2 (MM).........0.1

This favors the phono stage, TT and arm over the cartridge more than NickT's list, extremely so in the case of the MM (thanks, Raul!).

The sound with either cart is phenomenal. You'd expect that from the $4,000 LOMC and it's certainly the better of the two, but the real lesson is how great that little MM sounds. No one would guess they were listening to a $100 cartridge in a $20,000 front end. This crazy cost ratio (top class components, throwaway cartridge) works remarkably well.

OTOH, every time I plug my world class LOMC into a system with a lower quality tonearm, turntable or phono stage the results range from boring to terrible. Very revealing cartridges reveal system weaknesses just as well as they reveal music. Do not make this mistake.

Get your other components above the level of your cartridge or you'll never hear what it can do.

Dear Doug, Your argumentation looks very 'sound' but presupposes much knowlege about,say, analog 'experience'.
I,for example, know that Van den Hul 'swears' by Technics
EPA-100. I would never dream to pretend to know beter. But I bought the Triplanar VII wich is ,say, 4 x more expensive because I regard this tonearm as the most beautiful ever made. But your 'cost-ratio'argument
have some other support. One Dutch firm bought an very expensive 'machine' ($ 20 million) but this machine 'refused' to work. So they asked for an specilist
who give an rap to the macine in 'some place' and the machine was working. But he made expenses claim for $ 4000.
To the questin:'$ 4000 for an rap?' his answer was:'the
rap is $50 but the knowlege where to apply the rap is the
Thanks so much for the thoughtful comments. I am largely persuaded that upgrading the arm should be a priority, and probably the phono stage, too (which I suspected.) Unfortunately, the Thorens is not the best platform to "build on", as it is limited in the arms it will accommodate, only Rega-type or SME (with a different arm mounting plate, which takes almost 6 months and $200 to get from Thorens.) fwiw, the low output Grado Ref was described as a "budget" cartridge by a knowledgable distributor, and it exhibits slight sibilance in my system; it is good to know it is probably not the most limiting factor in this setup.
Dear Llydc: +++++ " the low output Grado Ref was described as a "budget" cartridge by a knowledgable distributor " +++++

that does not surprise me coming for a " knowledgable distributor " that for that statement and with al respect he is more on the unknowledge side than in the other one.

Maybe a 1.5K cartridge could be name it a " budget " one because that price against cartridges in the 5K price range ( and I can understand this. ) but as Doug point out:
+++++ " Aiming for some cost ratio is largely pointless, since the performance and compatibility of components cannot be judged just from their cost " +++++

Yes, I agree with you: your cartridge is not the most limiting factor in your today set up.

Regards and enjoy the music,