The RB300 is a very good tonearm. Your money will be better spent somewhere else in the chain. Get a decent tubed phono pre or a new cart, as Jake suggests.
Tone arm upgrade
I'm currently using a Rega RB300 modded tonearm ( aftermarket wiring harness and counterweight). I'd like to consider a step up, have been keeping my eye open for a good condition used Linn Itok arm. Is this the right path or in the $1~$2k price range is I there another good alternative?