Next upgrade?

Just looking for an opinions on what my next upgrade should be. I have a VPI HW-19 Mk. III with a Rega 300 tonearm. The cartridge is a Grado Reference Platinum. This goes straight into the phono section of a Mcintosh MA6900. I have about $500 to spend on an upgrade, and didn't know where to go next. I'm leaning towards a new cartridge (Dynavector 10x5) and getting a Mint Tractor to align it. But maybe all I need is a phono stage? Any help would be appreciated. Thanks!