Where did you get 見放題 from? The meaning is completely different. 観光 being sightseeing, 見放題 being "see as much as one pleases". Of course they are not interchangeable. The only use i can imagine for 見放題 at the moment is some web-site, where you pay once and then have unlimited access to all the media (videos or images). And perhaps some adult oriented services, like striptease, peeking etc.