Our core business strategy was built round the process you describe.
To keep it clean and to focus our minds we separated the parked domains into a separate company and the developed names into another. This way each company could 'buy' the domains off each other for what they were 'worth'
The company that develops websites has a team of editors and linguists that develop and manage content etc, everything else is subcontracted out - in the main to Russia and Romainia. We have defined three core types of developed websites and all our developed website fit into one of those models.
The company that parks domains has no resources to speak and relies on a combination of automated processes and (mainly) my time. the parked website are built by a reasonably good sytem that we developed ourselves but a lot more of the non creative (i.e. technical) process could be automated.
This has been pretty sucessful and we have a network across the UK, France, Italy, Holland, Spain and Germany with widely varing results across different countries.
However we have hit a problem! The value of the developed sites in all but one or two (what look like random)cases has been much greater than parked so even in the company that is the 'parking' company there has been a tendacncy to 'drift' into developed sites allthough not on the same scale. Because of a package of domains we acquired the parking company has also moved into local search and shopping comparision.
We think the future for us lies in having much better automation and contol over all our sites and so our aim now is to:
1. make our developed sites mcuh more credible and authoritive
2. make our parked sites much more like our current developed sites (maybe using the old processes from the developed site company)
3. reduce ir eliminate our reliance on affiliate or ppc networks by increasing radically the amount of advertising (in whatever form) that we transact directly with advertisers rather than though a third party (to this end we have invested hevily in our our advertisng network technology)
4. hammer local and shopping search.