I am a fan of the points system, so my bias is to advise you to enroll. Essentially, they are offering free enrollment. No guarantee what the offers will be in the future. Even if you are paying the $175/yr for the next ten years for minimal exchanges, you are still paying less over time than the standard up front enrollment fee.
If you are enrolled and have a DC Points account, then you should be able to rent points even if you have none of your own. If you think you will opt to rent some points on a semi-regular basis, if it were me, this would be the most compelling reason to take the free enrollment option. If you are not enrolled and don't have a points account, all you can do is have an existing points owner make the reservation for you. They are your landlord. When you are enrolled and you rent points, as soon as you pay for the points and the seller transfers them into your account, they are YOUR points and you can make your own reservation just like with points you own. You do not have to worry about having another owner as your landlord and just being an additional name on their reservation - the reservation is yours. That would be a very important consideration for me because I prefer to control my own reservations.