Hi Rob,This probably too late given that its almost the start of the season:-) Bungholio was built using a male mould and a similar layup with 2 layers of 200gram e-glass on the outside with a 10mm 80kg/m^3 herex PVC foam and 1 layer of 200gram glass on the inside. It has lasted very well and won the NZ nationals in 2010 at the age of 10 years.
The compression dents and delamination are a function of the core compressive strength and the outer skin thickness and strength. For a javelin its very easy to make them stiff enough but harder to make them robust enough to impact. I would avoid using kevlar in the outside skin as it makes repair much more difficult, but it has been used successfully in javelins in the past and does improve the impact resistance.
If you have any javelin questions ask on the javelin e-mail list see WWW.javelins.org
Dave Lee