I come back to the fact that there are good retail businesses that want to set up on the high street. I see no reason to provide discount-rates for offices when there are retailers who would be willing to take the units.
The empty retail units opposite the station on Perry Vale are in a great location, particularly for the morning and evenings. I could easily imagine that a coffee shop would be perfect for such a location, rather than the location of some of our fine coffee shops (half way up David's Road for example). Not that we have a shortage of coffee shops, with another new one opening at the weekend in the pool, but I think some people are a little too quick to write off the high street as a concept.
Forest Hill town centre is going through a period of transformation, many businesses closed over the last 10-20 years, but in the last few years we have seen new retailers opening up led by the pubs, cafes, and hairdressers, then boutiques, delis, and other niche retailers and services.
In the particular case of the units opposite the station, I don't believe they should have been allowed to be built without frontages and services installed. By avoiding this work they avoid paying business rates on the empty property and there is no incentive to reduce rents to attract businesses, especially with the up front cost of kitting out the units from nothing.
There are other retail units where conversion to offices would be sensible, the shop on Stanstead Road that has the application for a business business is an example where this might work well, without impacting the retail concentration in the town centre.