The DLA compounds I released way back and polygonizer got to this result in minutes... I would treat the "ribs" as a different problem (if I couldn't simply make them by hand) and use an l-system approach to make a branching structure and then deform it to the shape of a sphere much as I've deformed the DLA here to fit to a hidden polygonal "egg" shape.
By using the compound in a simulated ice tree with number of iterations set low, you can get a "growing" animation, or if you just want to calculate the whole result in one go like I did here place your tree in the modeling stack.
