I mention the money because this riding tour can be pricey if you are taking your whole family. But for $50 per person (children may be cheaper), you get a very thorough tour of the botanical gardens.
One possible negative is that, for our tour at least, the tour guide did not pay attention to the clock so our 2.5 hour tour ran over 4 hours! We loved all the additional information and opportunity to get off the trolley and look at plants, but you might have found it frustrating if you had a date to be somewhere else. My advice, if you are time-constrained, tell your guide. Even better advice, sit back and listen to the stories and take lots of pictures.
High point for us were the baby albatrosses. Who'd have thought we could walk up as close to them as we wanted? It gives you some idea how threatened they could be if people let cats and dogs run around.
They also offer walking tours. I don't know how much less you'd see. The covered carriages will keep you dry in light rain. They also have umbrellas for the passengers.