Do culture points 'roll over' if you opt out of adopting a new policy?
Solution 1:
You will accumulate Culture Points even if you already have enough points to buy a policy. This can be very important strategically:
If you build the Cristo Redentor Wonder (or are close to building it) you should wait to buy your policy until after it's complete, in order to gain the 33% discount.
If you build or annex more cities the cost of future policies goes up, so you should purchase your next policy before obtaining a new city.
As far as not wanting any of the currently available policies, sometimes you have to just take a non-ideal policy to open up future policies you DO care about.
Solution 2:
The culture points are still accumulating, you can spend them at any time you want. Just be careful, if you build a new city in the meantime the cost for the policies goes up.