I was debating what to do with my DL Gold ... they sent me an offer of 15K miles to upgrade to the DL Plat card (I know the signup bonus is a lot more but I'm gardening for a new car purchase next year, so no hard pulls). ... so I went ahead with the upgrade.
That hurts to read, considering a DL Plat sign up bonus can be 70-80k lately. Also auto loans aren't very sensitive to HPs as long as you have a good credit score. My Mom recently received a similar upgrade offer and when she told me about it I told her to shred it since it's not worth it.