How not? You get royalties from their project and, if they succeed, you will be able to negotiate that for more than you have paid. And there is a possibility to receive ownership, I do not know if any of the recent ICO has given that, but they could; future products or services for the Token that you have bought.

No, that's not how the majority of ICOs work. You get no royalties. The tokens can be anything.

https://omg.omise.co/ OMG holders can use OMG to validate the network. If they validate a block correctly, they get paid the tx fees from that block

https://blog.golemproject.net/golem-network-token-gnt-sale-2... All transactions in the Golem network will be subject to a fee, approximately 5% of the transaction value. This will include both transactions between the users — payments for computing power — and transactions between users and software developers. The latter will consist of payments for the software used on the Golem network in a SaaS model. Where applicable, a blend of both open source and proprietary software will be used.