Should I trade-up from my Krell KAV 300?

My system is a Krell KAV 300, Meridian G08, and Thiel 2.3 speakers. My interconnects are Creative Cable (Music Direct used to sell them for $375). My speaker cables are Synergistic Research (about) $500. My room is small and I listen at relatively low levels, mostly classical piano, some symphonies.
Should I invest in a used Krell KAV 400 or instead invest in better interconnects or speaker cables?
Thanks for your help.