Like most things in life, it's something in between! I think it's safe to say that very few managers spend the maximum in scouting every week. It really depends on your context. If you're not going to do too well in the league you may end up with one of the top picks, so it's a great chance to find a good prospect. Still, I think it's always useful to invest in scouting. In my own case, last season I spent 20k a week and picked third from last, but still picked a good prospect, that is/will be worth more than the 20x14 weeks = 280k invested.
Another word of advice is to not start spending scouting points as soon as the list becomes available. There are two special combos (explained in the draft page) that can be pretty useful, but they're only available after the all star week.