I am one of the "existing observatory lessees" that Madhup talked to. We've had our observatory up and running at RH since 2010. We're also a lot owner - we bought the land for our retirement, *then* found out about the remote observatories. Feel free to PM me with questions about RH.
>>IIRC it's not possible to own an observatory at RH without buying one of the residential lots.
Not really - people like Madhup can build an observatory at the observatory site without buying land.
The lease model at RH is different from other sites such as New Mexico Skies: support is present but limited to ensuring the roofs operate and address minor issues like cable snags, retightening loosened items, plugging/unplugging cords, etc. Any equipment configuration and major troubleshooting is usually the responsibility of the lessee. Though the lessees have formed a mutual support group as well, in terms of whoever is visiting can help others with minor issues.
The skies are definitely worth it:
The Greenwich Observatory has an annual Astronomy Photographer of the Year event, and for 2014 one of the observatory owners won the Robotic Scope category: