Not all the apps pay for delegations. But curating can bring a lot of profit to investors for sure. And if they will create some content of course they will be supported very well. If I had about $100k I would invest it in steem, it could make about 333k sp and it's possible to earn from that more than 1000 sp curation per month, but again, if the price of steem will go lower, so I will have less $. So, investing in steem is very profitable if the price in $ will go higher, and more likely it will go soon because bitcoin is growing and steem will grow as well.