All those suggestions don't really inject elegance. Elegance in writing involves not lavish use of extra words, but concise use of precise words, used gracefully, to communicate anything you want, emotions or thoughts, concepts, principles, axioms, whatever. Elegance in writing is a taking away of nonessentials until what is left is perfect. Using more words than necessary just makes writing turgid, opaque and pretentious.
"Ask not what your country can do for you; ask what you can do for your county" is an easy example of a few words conveying an entire philosophy.
If you want to gracefully express yourself in a thank you note or anything else, it is very helpful to put the 19th Century paradigm of etiquette into your head. It is not a bunch of rules about which fork to use or whether to use "my compliments" or "my respects" depending on the social status of the recipient; it is simply phrasing your thoughts and behavior to never make the other person feel at a disadvantage. Your exchange is all about them, nothing about you. Don't talk about how you feel (shaky ground for us, right?). Talk about the thought and care they put into the gift you received, the work they put into a graduation or promotion, the strength it takes to carry on after the death of a loved one or loss of a job or divorce. You can be guided by your emotions - you might feel sad for a loss, happy for a gift, etc. - just don't talk about your own emotions. That's grace.
The final ingredient could be tying yourself to the occasion: "I can never think about your father without remembering the time we ripped a plank on his boat on a snag and had water gushing in. He just lit his pipe and said, "Better bail faster." "I will think of you every time I bring in a brookie on this fly." "Senior manager? Every now and then management does make the right choice! Your company is stronger for your promotion." Write about your memories or thoughts; your emotions will guide the selection.
I trust this makes sense. I'm rushed, late to an appointment, but i couldn't let this slide. :-)