What are the best places for wildlife tours that haven't been used that much yet? Considering safety and environmental balance, of course. I think there aren't that many, unfortunately. For example, Galapagos is beautiful, but there's too big a risk of irreversible damage to the environment.
I would think places in Africa that are still bastions of charismatic megafauna. Some countries (like Kenya, Tanzania, and South Africa) have really capitalized on those resources tourism-wise, while other countries like Gabon and Botswana have similar endowments but not as much tourist infrastructure. New Guinea is another location that has high potential for ecotourism, especially for birders. Perhaps this is due to instability in some parts of the region, but I think more wildlife tourism could be supported in the mountainous regions of Central Asia. Or perhaps in the boreal forests of Siberia.
Main threat to Galapagos are actions of local people, who do everything from overfishing, through casually introducing exotic species to purposefully killing giant tortoises to spite the conservationists. Galapagos is a sad case: well-meaning people are asked to support nature protection overseas, but are hit back as they are overpriced or banned as tourists, but the actual destruction of the place continues by local power, so to say. Your actual question: Places with rich wildlife, politically sfe and accessible: In Europe, West Balkans, Romania, Bulgaria, Baltics, Belarus, Ukraine, Georgia, Armenia and Kazakhstan have good wildlife but are undervisited. On a different scale Mongolia has great empty wildlife areas and is politically stable. Myanmar develops fast. Many parks in China have fantastic wildlife and good tourist infrastructure for local Chinese tourists but are un-visited by Westerners. Ethiopia. Whole Eastern India - Bengal and eastern Himalayan states. Gujarat. Botswana has fantastic wildlife but still complains about too few tourists. Peru, Colombia, Guyana, Chile and Argentina also have wonderful habitats. Eastern Europe, Botswana and South America are especially good, because individual tourists can travel and experience them on their own, rather than being forced to use pricey organized tours. I would point jokingly that many national parks in Canada and U.S. West have lots of untapped wildlife potential. Trails, hotels and areas of legal access are unnecessarily concentrated only in small parts of wide areas. Main famous spots are horribly overcrowded, but nobody ever goes even a mile further.