Cartridge or external power supply upgrade

I have a newer Nottingham Spacedeck with Shelter 501 cart. I am looking to make the next upgrade. I have considered a Walker precision motor or upgrade the cart. to a shelter 7000. For those of you familiar with the neuances of analog sources which do you feel provides the most improvement for the money, cart or powersupply. I have already upgraded the base to a SRA that was custom made for the spacedeck. Thanks.
My guess would be to get the better cartridge . i have a simon yorke with a walker motor drive & a kondo io-j ,if i had to get rid of one (or downgrade)it would be the motor drive NOT the cart.
I agree with Honda. A cartridge change should make much more difference. It's a proven fact that cartridges, room acoustics, and speakers have the widest variability in performance. I have used the Walker motor drive in the past, and more recently the Shelter 501. I never quite warmed up to the 501.

Great pic of your son and family dog praying together... That's priceless!