Both uses of the past form are possible. Some grammarians speak of the past form as "remote", because it "removes" the verb to a distance which may be either temporal or social.
Hi, Maria, I'm calling because I wanted to take you out for dinner.
Here you use the past form to make want less demanding. The remoteness is social.
Sorry I couldn't track you down last night. I wanted to take you out to dinner.
Here the primary sense is clearly temporal remoteness. You could, however, work in a degree of social remoteness by also employing the progressive construction, which in this case would have no implication of imperfectivity - it would just be a further distancing device.
Sorry I couldn't track you down last night. I was wanting to take you out to dinner.
Note that this last construction could also be used in the first example:
Hi, Maria, I'm calling because I was wanting to take you out for dinner.
In this particular instance, however, the progressive construction would probably not be used because it clashes with the progressive calling in the main clause.
- Grammarians give this the Latin name horror aequi, "the
widespread (and presumably universal) tendency to avoid the use of
formally (near-)identical and (near-)adjacent grammatical elements or
structures" (Rohdenburg).
You'd be more likely to use it in a context without a prior progressive:
Are you by any chance free tonight? I was wanting to take you out for dinner.
To express the "see-what-you're-missing" sense in English you would employ a construction with a stronger sense of intention. The past would be necessary in this case, rather than optional, because you would be speaking of a prior intention which no longer holds:
I was going to take you out for dinner, but I've changed my mind.
The locution "of course" is neither polite nor impolite. The tone in which it is delivered makes all the difference.
Did you like the movie about swashbuckling pirates?
--Of course, I liked it, matey! You know how much I like to talk like a pirate, arrrh!
Would you like to come with us to the concert? I know your car is in the shop.
--Of course, it's so nice of you to offer.
Do you like those cookies I baked for you?
-- Of course I like them, it's *my* recipe after all! Why wouldn't I like them?
Best Answer
Alternatively one says "They have ruined my reservation" or "They have messed up my reservation". Hope these will help.