There was a piece on the WSJ this week by Scott McCartney about using airline miles for merchandise rewards such as hotel nights or car rentals (you can access the article here). This is about the worst way that you can use your miles. Period.
The article is partially based on a study done by IdeaWorks about Best Value Rewards using airlines miles that you can access here.
Airlines and some hotels loyalty programs (Marriott and IHG Rewards) allow you to use miles and points for merchandise and airlines to hotels and car rentals, and hotel programs for paid airline tickets.
Airlines miles are still worth most when used for airlines tickets (business and first) and hotel points when used for hotel nights.
The article discusses the discounts that some programs are offering for their elite members that redeem for merchandise and in case of airlines for hotel nights and car rentals.
If you really have more miles and points that you can ever use, then it might make sense to redeem for merchandise at terrible value. At least you get something in return. This should not, however, be the default mode of redeeming for anyone.