Under a $1000 might just be a lateral move soundwise, but for vibration/stability etc. I'd keep an eye out for a used SL-1200 (MKI or II). Built like a tank, sounds amazing, plus the ease of switching out headshells with different carts is brilliant (one of the main reasons I love it).
Upgrade from NAD C558
I went from a VPI hw19 Mark 4 down to a NAD c558 when I downsized. Oddly enough in between I had a Rega RP3 which I really didn't like at all despite its accolades. Anyhow, I run both MC and mm cartridges and looking for something new or used under a thousand that would be an upgrade in terms of stability, vibration and tonality.