After 15-20 solo trips, I've dined at lots of WDW restaurants, but only one of the 3 you mentioned-California Grill. That was great-when they saw I was solo, they gave me a lovely window seat where I could watch the monorail and the gorgeous view. Excellent experience. I've also eaten solo at 2 other signatures-Jiko and Narcoose's. Great there also. At Jiko, the salad preparer was testing a new salad, so she asked me to try one (no charge) to "test" it.
My only negative experience was at Chefs de France, where my server was too busy flirting with the young, pretty girls at the next table and pretty much ignored the dumpy, grandmotherly type solo.