Question about my Grado ZF1 phono cartridge

I'm trying to get my stereo system back in shape.  My AR turntable has a Grado ZF1 cartridge in it, and as far as I can tell, it sounds dull and flat. This is going through a new NAD C165BEE preamp with the resistance set at 600 ohms (R1) to get the best sound possible, and it still sucks.  The cartridge is old but hasn't been used all that much. They don't sell these any more and I can't find any info via Google. I'm wondering if I get a Ortofon 2M Blue cartridge if it will be much of an improvement.  I don't listen to my vinyl often enough to justify spending more than about $250 on it, and I think that would be a good choice.  But I don't want to waste the money if it won't be any better than what it's replacing.  Sound through the system using CD as the source sound nice and bright, so I know the fault lies with the turntable.

Thanks!