The fixed ideas you describe probably originated from earlier calculus courses where students were exposed to "vectors" without any reference to vector spaces.
You could try some decontamination by first introducing groups, rings, fields and modules, before proceeding with vector spaces. Of course I do not suggest to turn the course into abstract algebra by going deep into group theory or ring theory; just giving a few definitions, plenty of examples and some immediate results, should be sufficient.
I see the following advantages:
the students meet something new right in the beginning, so they are less likely to fall into the "Oh, I already know this"-mode.
later definitions e.g. of a vector space can be build on previous ones and grouped into meaningful parts.
results like e.g. the homomorphism theorems can be given several times in slightly different situations.
The main problem with this approach is the danger of running out of time.
