Hi there,
Yes, give the students a better reason to read the passage. For example give them a time limit to find four words that start with the letter F, to find three irregular verbs and an adverb starting with S.
Your treasure hunt task can be related to language points that are being worked on in the unit, or for revision.
Another idea is to give a short time-limit that just gives enough time to read the passage. Then all students turn their books over. Pick out one student to say what happens in the first paragraph. Then a different student to describe the second paragraph and so on.
They probably won't do this that well the first time so have a re-run, with the same passage. This time they will do better.
For many more ideas like this to help students be more implicated in their own learning do check out my games books. For you I would recommend the teen/adult games book rather than the primary ones.
This is the page for it and there are free games that you may receive by email to try out:
ESL Games and Activities for adults
I hope you enjoy the ideas and that you can get your class more motivated.
All the best
Shelley