On another forum one person was talking about how he had a rabbi friend who would say "Happy Hanukkah" to him even though he knew he wasn't Jewish. When he brought it up the Rabbi said "I didn't say you celebrate Hanukkah, I'm just saying I hope you have a nice time around Hanukkah" (or something like that).
If the Rabbi is being inclusive and is welcoming you to celebrate with him ...who cares?
If he were to invite you to a Chanukka feast, would you go even if you were not Jewish?
I agree with you in this thread 100%.
I use "Merry Christmas" and "Happy Holidays" interchangeably even today and even with my Christian friends. For one thing, we have two holidays at this time of the year. Three if you stretch it from Thanksgiving. We have a religious holiday, Christmas, and we have the secular holiday, New Year's. So, if I say Merry Christmas am I really saying, "Have a splendid Christmas, but I hope you have a shitty New Year"?

When I say Happy Holidays, I am thinking the entire holiday season which for me is basically from Thanksgiving through New Year's Day.
Typically, I start the season by saying "Happy Holidays", around Thanksgiving, I'll say, "Happy Thanksgiving", then go back to "Happy Holidays". As Christmas approaches, I start saying "Merry Christmas" and finally end up with "Happy New Year's" and end it with... "pass the <<latest hangover remedy>>"...
Like I said earlier, I don't care what kind of greeting I receive from people. The only thing that would bother me would be a business establishment forbidding their employees from actually using one for PC reasons. If Best Buy has told its employees not to use "Merry Christmas" that bothers me (and Best Buy) is where I like to shop the most. I was at Walmart the other day and upon completing my purchase wished the cashier a Merry Christmas... the look I got was like that of a deer in the headlights. Oh my gosh, what was he supposed to say??? I got a "good night come again" kind of response... that is sad.
That is not to say that there is a war on Christmas, but, I would love to see a "War on PC-ness"! Give me a break. It should not be such a big deal to say Merry Christmas or Happy Holidays.
As for your question about attending a Chanukah feast, I can say that as a Christian I have been involved in Chanukah celebrations before as I worked for a Jewish Community Center for a couple of years. I was also privileged enough to attend a Passover Sedar with one family and I would go again if invited. It was not only a very good time for my family, but it was a learning experience for us all.
Immie