I think it depends on how confident you are in your vacations plans in the forseeable future. For example, are you sure you want to go once a year or do you think every other year is more your speed? Are you sure you need a two bedroom or will a one bedroom or even a studio work? Will you be going for a full week or do you think you will switch to shorter (or longer) visits? Will every vacation be similar or will you mix it up with villa size and different lengths of stay?
If you are very confident about your answers for the next, say, five to ten years, I would purchase that amount of points. However if you are unsure, you may want to start small and add on if it makes sense. It is easier to add points that to reduce the number of points you have.
Also in regard to the last point, if you think you need 360 points because you plan to stay in a 2 bedroom for a week during the summer at AKV SV every year, don't buy as one big contract. You cannot break up a contract so if you later decide you don't want to go every year or that you no longer need a two bedroom, the only way to reduce your points is to sell the whole thing (which will be hard because many people do not have the cash to buy that large of a contract on the resale market) and purchase a smaller contract - expensive. Instead, break it into 2 or 3 contracts - say 160, 100, 100. Then if you later determine you only need a 1 bedroom for that week (268 points) long term (say after the kids are grown), you can sell one of the 100 point contracts.