Re Staff West - it won't be a bad accident as speeds are likely to be low, and seat belts/airbags etc. will save people from injury. Inconvenient yes; bad no. Not to detract from the fact it's always been a crock of ****e.
Re AVP - I seem to recall there's a planning permission/use classes issue, that as it's ancillary to the airport it can't be allowed to get too big in its own right, otherwise it becomes a tourist attraction or something, which isn't what the airport is for. It's an airport, not a leisure destination. That'd mess up the traffic volumes for the M56, air and noise quality, utility services, drainage and so on.