There is a new car rental offer that is good for 25,000 miles with an Avis rental of 3 days or more. Just like the last time they ran a promo like this, you will have to be able to book quickly and the travel window is relatively short, but this offer appears to be repeatable for up to 3 rentals, which could be a great deal if you need the car rental anyways.
Platinum Co-branded Credit Card Members will earn 7.5 miles per USD spent
If you can get a decent price through the portal, you will be able to reduce the cost of your car rental.
With this promotion, you get a good deal. There are still a number of places where you can use Etihad miles for premium cabin international travel, such as 22K miles one-way in economy class from the east coast to Casablanca on Royal Air Maroc, or 44K miles in business class. You can find EEtihad Guest sweet spots for award tickets in business class or economy.
It wouldn't be hard to get at least 1c per mile out of the miles if your partners fit your needs. It's worth at least $250 to people who can use the miles.
The booking page doesn't always give the best prices. I looked up 3-day rentals in several different cities and came up with prices between $200 and $250. The combination of a 3-day rental and 25K miles at those prices makes this a great deal if you really need a rental.
You will want to look around. If you're looking for a better deal, you should check the prices against Autoslash. It would have to be a big price discrepancy to make this deal not worth considering. It's a good idea to shop around, but this deal looks good to me. Make sure you check the terms before you rent a car.