Not the best.

I'm surprised that the motor is only rated at 60V... whoops... a quick google confirms someone else with a VMC190 with a 60V spindle... so let's go with that.

Using a standalone PSU you've only isolated the supply to the spindle - in other words isolated the spindle from the RCD. You[ve not fixed anything, just avoiding the protection normally offered. Did you get around to cleaning the spindle motor?, or testing the Lenze?

(full disclosure: I did pretty much what you're suggesting - replacing a spindle motor and controller card when it was cheaper than replacing the OEM controller card - so call me a hypocrite)