I'm in both camps on the ice plant. Visually it's better with the ice plant, but the hole plays much much better without the thick layer lining it. The green's too narrow to have that kind of penal hazard attached to it.
For what it's worth, if I had the chance, I go 50-50. Pebble is very top heavy. Holes 4-10 and 18 are true world beaters (but I still think they could be better) and a few of the inland holes like 3,13, and 16 are very, very good. But 1 is unbearably awkward for an opener, 2 is meh, 14 and 15 are terrible, and 17 has lost everything that once made it a great par 3.
Spy doesn't have the firepower of 4-10, but there are so many good holes there, and very, very few weak ones. Spy is definitely the more difficult course and for what it's worth I think would set up really well for the pros. Ask yourself, would a slightly altered Spyglass or a heavily altered Pebble Beach work as a better host for the US Open? I find that only awkward hole is 16 (I feel like it's a much, much longer version of 1 at Pebble) and 18 (which, particularly for a finishing hole, couldn't be more boring).