My Peachtree Nova 150 MM phono stage versus a standalone MM phono preamp?

I'm trying to determine if the phono stage in my Peachtree Nova 150 is as good as any commonly available < $500 (my max budget) phono preamps. 

I have a U-Turn Orbit turntable with an Ortofon Red cartridge connected to the Peachtree phono stage via Audioquest Cinnamon RCA cables and it sounds pretty good. But I'm also curious whether a standalone phono preamp up to $500 would be better than what I already have?

When it comes to specs for a phono stage what are the most important numbers to look at and compare? Should I consider replacing my Ortofon Red cartridge with something better first? Or just save the $ and use it to purchase more vinyl because the hardware I have is good enough?