It really depends on your 1 1/2 year old.
I think some kids can get easily scared.
Its up to you, but my advice would be to take your 1 1/2 yr old to see some large characters up close before you get to Disney.
We took our outgoing 9mo old and she had an absolute blast with the characters. Smiling, giggling...
She went back at 13 months and she was a bit scared at first, but then warmed up and had a good time.
This summer we took her to a chucky cheese so she would get used to some large characters before Disney and she was terrified by Chucky at first. Again, it took a whlie, but she finally warmed up.
We are going back this November and she'll be 22 months. My guess is that the first sight of a 6 foot Tigger or Pooh coming up to her will scare her, but she'll quickly get over it.
As far as restauraunts go
Your 1 1/2 won't miss much with the Princesses. Don't get me wrong, they are great and the concept is great, but kids don't really get it till 3 or older. I'm sure others have differing opinoins.
All that said, we are trying to get Cindy reservations for our Nov trip
Our favorites would be Pooh at Crystal Palace at MK - but its currently closed till Dec I think.
Pooh has moved to Tony's and we have PS there in November.
I've heard good things about it.
But my daughter's favorite is probably Mickey at Garden Grill for lunch. We have had our best character interaction there.
Personally, Garden Grill is not my favorite place to eat, but the characters there have always been great.
We were not impressed at all with Breakfastasarus at AK.
I've heard good things about the Poly and like the other poster, there are some positives about family style so you don't have to leave the table.
have fun!