Unless this couple is in the habit of throwing themselves parties and expecting gifts I see no reason to consider this a negative.
Renewals aren't uncommon. I've never heard of one being used for a rocky marriage. They are normally just done as a recommitment and many people do them on their 10th, 25th or some other one considered significant to them.
IMO you don't need to send a gift. If you feel you need to maybe a gift card to a nice dinner they can share. I
would send a card congratulating them on 10 or 25 (whatever) years.