I agree with Manon. 2 points is almost always the correct option.
Having said that, I switched to 1 point for a week last season because I like to have an even number of points. I've no idea why, I just do.
The only reason I can see for spending more is if you're going to be guaranteed a good pick (personally I'd only do it for the No 1 pick) and you need more points to scout.
What everyone should do when spending points of the draft is consider the cost, and consider what you will get out of it in terms of value. Whether that value comes from selling your draftee, or from the amount of money you're saving by not having to buy a player.