These Delta Gold offer come around often. I get them every other month. They ranged from 50k to 75k sign up bonus offer.
The 75k offer is the best you will see from a Delta Gold card.
I would wait until early February, since that will give your file some more time to age.
In the interim, between now and the app DO NOT mess around with any AMEX cards review, no checks for "I wonder if I am prequalified, this won't affect my credit" on their web site. You have a specific targeted offer and you want to keep that from getting messed up. There are several reports of people who had targeted mailers, were uncertain of their chances, went in to check AMEX prequalification, and AMEX later said, "sorry, you used a prequalification tool. That reset (ended) our offer to you. The mailer is no longer valid".
Just trust that you will be granted the card with $1k or possibly a $2k limit, and give your file a bit more time to age. Then enjoy the 75k bonus miles and card benefits.
I wouldn't apply to it either unless you are already an AMEX card holder. I got targeted too and will apply because I already hold 4 cards with them so the chances of another offer like this 75k is rarely going to happen to me.