I don't know if 10W-30 is too thin but I'm pretty sure it's not on MB's approved oil list for use in Miami. Even if the plugs weren't fouled I'd switch to a -40 or -50 oil ASAP. I can't read oil labels and I avoid oil threads so I don't know if 0W-40 and 15W-50 synthetics are thinner or thicker (more or less viscous?) than 10W-30. 10W-30's Honda oil
More than a quart in 1000 miles is cause for concern in my book. Again, even if the plugs weren't fouled I'd look into doing something about it.
Any chance of a picture of your plugs?
I think at the point that you're running rich enough to have chunks on the plugs you're probably leaving a trail of smoke that would shame a Diesel.