If this is a step towards a long term hi-end system then I would get the highest quality tube preamp I could afford. This pieces is the heart of the system. From there you can work on source issues. The cartridge is certainly a key piece if your focus is vinyl. I would not spend money adding a better arm to the Rega table. You did not mention speakers. You must be happy with them. They are the most critical part of the chain.
New preamp or up grade my cartridge and or phono amp?
I have an Emotiva XMC-1 with a Rega P6 TT a Rega MCFONO phono amp and a Rega Ania cartridge. If I'm running the Emotiva in the "reference mode", would it make more sense to up grade the cartridge and phono amp (maybe even the tonearm) or add a new preamp with a HT bypass