Hi Happyeater, Floor care and floor maintenance is a big topic, so I will try to keep the response short, if you want further advise please contact me off line for a general discussion.
4-5 coats of finish is not very much, the polish will not give depth until 4 coats and you should aim for a minimum of 7 coats, the floor finish should provide traction and should be well maintained.
Always dust control before you begin your maintenance program.
Your scrubber dryer passing at about 400 rpm and with a non complimentary product is probably wearing the top coat away, and I would guess that you are down to the tile in some places, use a 20p piece to test the depth in the high traffic and against the edges, scraping about 1 inch in each of these areas.
Your buffer (1200 rpm burnisher) should form part of the maintenance program, I use LiquiMax From Buckeye in the USA, importing it directly, it has an 18 - 36 month strip cycle, Microabrasion resistant (Scrubber Dryer damage), Self-levelling when applied and maintains without ridging, does NOT powder when burnished, does NOT yellow over time I have found that a good product will save money and provide the best results in the long run.
Hope this helps Geoff