I can only comment on bluezoo and Il Mulino. I think they are much better than Disney's signatures. I don't find the prices out of line for what I pay for nicer meals anywhere else I eat.
I'm not sure which restaurants you are talking about but I did eat at BlueZoo, Picabu, and the Fountain at the Dolphin. BlueZoo was really good (but I wouldn't go as far to say it was on par with a signature restaurant), Picabu is just their quick serve restaurant and it is ok, and The Fountain was terrible.
If you are wondering if the certificates are worth it, check out the prices for the restaurant you are interested in on allearsnet and then see if the certificate is worth it.
But now I think I'll have to check it out for myself
We ate at Il Mulino last week and it was one of the best meals I've ever had at Disney. Not only was the food wonderful but the service was even better. Would definitely eat there again.
We've dined at Tod English restaurant in Boston "King Fish Hall" with a restaurant.com gift certificate. It was fabulous. This year we came with our girls, fine dining is not an option. Next year we hit food in wine, just the 2 of us. Bluezoo is on our list. We love restaurant.com. We used it for House of Blues this year. I was blown away. I figured burger, fries and bar food. Go for it.