Since I make a living painting portraits, my circumstances might be a little different...
My little town of Peterborough, New Hampshire has an annual art auction for charity. The average bid generated from this auction is less than $200.
My average price for a portrait is $8000 and producing it takes months of my time, attention and energy...not to mention the high cost of materials. (Imagine how I'd feel if someone got $8000 worth of my work for a mere $200?)
My annual income does not support my making an outright $8000 gift to one charity. Therefore, I think that it would be foolish for me to donate a portrait to this (or any other) charity or auction.
For me, a 10% gift of the cash income from my work to charity makes a lot more sense. If there are those who think this is stingy of me...so be it.
In addition to this...I confess that I love to shop! I'd much rather poke around in little stores and find "just the right" gift for friends and relatives...alas, not everyone finds my work "precious."
Anyhow, this is just another viewpoint
....to each his own...