I mean that you might still send cards every year is a nice touch (and definitely far more than I've done in the past). And if you don't necessarily have a "close" relationship with anyone, then I think the card thing is a nice touch to have people remember you. I definitely have people I've only contacted in regard to "hello, hope all is well, would you be okay if I listed you as a reference? Thank you", so I think you're fine. Although maybe others may have different opinions!
Re: Question about quitting my job
I see!
I mean that you might still send cards every year is a nice touch (and definitely far more than I've done in the past). And if you don't necessarily have a "close" relationship with anyone, then I think the card thing is a nice touch to have people remember you. I definitely have people I've only contacted in regard to "hello, hope all is well, would you be okay if I listed you as a reference? Thank you", so I think you're fine. Although maybe others may have different opinions!