I get similar improvements using the ADH with my Raven One. However many Raven owners prefer no clamps or weights because of perceived losses in top end/ air etc.
In general the usual differences in taste, systems, turntable design and "voicing" apply here. No weight or clamp is free of coloration, but I hear nothing unnatural or amusical added when I use the ADH.
In particular the ADH provides a clear reduction in surface noise and certainly no increase in bearing noise due to the extra weight that I can detect. Noise and potential for damage of bearings are not likely to be issues with heavy unsuspended turntables like your VPI Classic.
I think HRS is just being cautious and conservative regarding the potential for damage to pivoting tone arms. I have no such concerns with my Basis Vector, which is essentially a unipivot.
Although the ADH is designed for unthreaded spindles, if you have no problems now with placing or removing yours on the VPI I would not worry about it. The ADH bore is lined with the same elastomer that is on its base. I suppose the thread on the spindle could abrade this elastomer if it was a tight fit.