Preamble: Once I moved out of their home, my parents didn't pay for anything for me. Even prior to that, in fact. I bought my own car with earnings from my first job. I paid for my own college, my own cancer treatment (Though I did move back home for about four months during recovery.) Hmmm, I bought my first house (and all subsequent houses) without any outside help. I paid for my own braces and travel. I finally got married very late in life and strangely, did not get any kind of wedding gift. Maybe they were mad because we eloped, IDK. (Don't think so, they loved DH. And I was too busy being happy to notice that there wasn't a gift. And no, money was not tight for them. They earned more in retirement than several of their children who worked full time.)
All along, my parents helped my sibs and their families. I was quite proud of my independence, and grateful for the skills they'd taught me so that I could be a successful adult - really, truly grateful, even though the above could read as a little bitter.
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Point: my mom used to send small checks from both of them for birthdays and Christmas, usually $25, occasionally $50. Once, after I'd done some big stuff* for them, she sent a thank you card with a check for $100, which was a nice surprise. In the past two years, both of my parents have passed away. ***I am going to miss those small checks at predictable intervals, even though I never needed the money.***
Take the gifts if it makes them happy and they can afford it and they don't compromise your integrity/independence. Someday your parents will be gone and you might wish you had. By then it will be too late.
*Funny, I can't remember exactly why, but I remember the unexpected check. I used to book all of their travel because they were not Internet savvy. I think I may have given them some free - oh, I remember now - a relative on the other coast passed away and I used my mileage to buy them last-minute, first class, round-trip airfare. It took some wrangling, but I was happy I pulled it off for them.