What a great analysis! Others would have made 3 posts out of those insights.
First time I hear about waivio.com. Pity it is not in Europe yet. May I ask how you have engaged those restaurants, did you actively went there and told them about the project? There are some restaurants in Europe, like @pizzajohn who might be potential partners.
Both Hive and Waivio are global systems. In fact, Waivio is designed as a multilingual system, where not just the interface, but news feeds can be filtered by language(s). Waivio is using Object Reference Protocol to post data (items, products, companies, lists, pages, etc.) on Hive blockchain and these objects can also exist in different languages. Once the object/item is posted on the chain, anyone can reference and use it.
Once the object is created, it can be referenced in Hive posts (by URL) and such posts will be linked in the Reviews section of the object (restaurant, product, item, place, etc.)
Rewards campaigns are also global. Sponsor can specify eligibility criteria for users and specify requirements for a review. And just post it on Hive.
Waivio is an open source project which is designed to be replicated.
Some guides chose to sponsor rewards campaigns out of their own pocket. And once they collect 20 or so reviews, they will present it to a restaurant and ask if they would like to continue the rebates program at, say, $5-$6 per new customer. There are many business options already available, such as excluding busy days (ex., Fridays & Saturdays), requesting a copy of the bill (with unique number), max monthly budget, registered upvoting accounts and more.