The land hadn't been prepared for the services and the northbound onslip still has a golf course between it and the rest of the site and a good portion of it is dense woodland. The two south-facing 'ghost sliproads' have since been put to use by connecting them to a new local junction, M1 J35a, which would have destroyed all other potential evidence for this once-planned service area. Around this time barriers were put across the two remaining 'ghost sliproads' to prevent them being used as lay-bys.
Although it all fits the bill, there is no hard evidence to suggest that this ever was planned as a service area. A junction similar to the current J35a was planned in the 1970s to form the eastern end of the M67. It's not clear whether this was the original (and possibly only) plan for the site, or whether the services and junction were planned to be integrated.
Pathetic Motorways - more information on the M67