What benefits to expect from tonearm upgrade

Puting arm/cartridge compatibility aside for a moment....
It would be interesting to have some more comments when we talk about "upgrades".
Most of the time we mean differences(that we either prefer or not) and yes, tonearms sound different from one another.
I'd really like to listen to a tonearm that will trounce a rega rb300 (in every respect) for example.I've tried many tonearms and all were different.

All high quality tonearms will improve with a better cartridge.The cartridge (correctly matched to a tonearm) will make the bigger improvement.Many years ago, a reviewer (if I remember well it was Alvin Gold in HNRR magazine)reviewed the RB300 and he prefered it to the much more expensive Zeta that was considered a reference back then.He also commended on the reasons why many dealers recommended the Zeta , presumably for profit reasons.Without a listening test on your turntable and cartridge you cannot be certain which tonearm will sound best.Not to mention that if we take vfm into consideration,things are much different,and certainly in favor of a better cartridge,even turntable...

All high quality tonearms will improve with a better cartridge.The cartridge (correctly matched to a tonearm) will make the bigger improvement.Many years ago, a reviewer (if I remember well it was Alvin Gold in HNRR magazine)reviewed the RB300 and he prefered it to the much more expensive Zeta that was considered a reference back then.He also commended on the reasons why many dealers recommended the Zeta , presumably for profit reasons.Without a listening test on your turntable and cartridge you cannot be certain which tonearm will sound best.Not to mention that if we take vfm into consideration,things are much different,and certainly in favor of a better cartridge,even turntable...or phono preamp.

I have set up my system very carefully and that is why I commended as I did.An SME V didn't do it when I was experimenting,as well as other tonearms.When I "tuned" the sme's mass to match that of the rb300 and my cartridges, well, yes the V sounded closer to the rb and for me not worth the extra cost.A tonearm in itself does not sound good or bad,it is the good pairing with a cartridge that does the trick for me,as well as the phono preamp as I said earlier.
By these comments,I must say I do not underestimate any tonearm's qualities , low or high cost.

Gondo101,
If you are happy as you say with your ortofon arm then a logical upgrade could be one of ortofon's own,or even Jelco's 12" versions.