I'm a bit late to this thread, but it's taking me several days to read through it in it's entirety (and tonight I'm backing up about 6.5TBytes of data to some external USB2 drives, so I've got a lot of spare time!)
HPC does have a certain something, but both directions that we use to leave are a bit of a hassle. Leaving southwards for Brighton, Bognor etc does give me a chance to use my rear light "laser of deth" to stop the traffic however.
I think that it's certainly worth trying out a few other locations, and conceivably a different location appropriate to the destination could be used each month. The down side of using different start locations, is that inevitably some people won't read the emails and will turn up to the wrong location (and I
really hope this never turns out to be me!)
Whilst arguably HPC is a little bit remote and quiet, that's why there's enough space for 100+ cyclists to hang around for half an hour, and then leave without mowing down too many pedestrians.