Personally I don't have a set rule to tip or not. It depends on where I am (therefore local custom; tipping could be an insult at some places) and the service quality.
I do concur the tip-dish is in poor dish. That said, workers in the CL at the Crystal Gateway Marriott use the tray for tip collection and soiled dishes. First thing in the morning for breakfast, I noticed several "single $ bills" on the tray. Subsequent visit to the CL saw the same thing. I suspect the workers might have planted them there to induce customer tipping. If I tip, I usually just leave money on the table, not to leave it at the tip-dish or a tray.