Well, maybe not ALL, but all I can fit into one of my days. 
UI sprites packed into an atlas, all other materials/textures are correctly instancing and taking up as few draw calls as I can manage, it floats around 15-30 per frame, at the moment, depending on activity.
My build size has doubled though because I'm essentially using two copies of the ground terrain mesh. It's a shortcut on the way to getting better performance... hahaha
First, I exported the Unity Terrain to .obj using this handy script: http://wiki.unity3d.com/index.php/TerrainObjExporter
(it's 10000x10000 units/meters) Then I took it into Blender where I, by hand(box select) cut it up into 110 pieces, so now I can assist with the culling with some simple distance calculations.
The reason for the doubling of the mesh is because I'm currently using 1 copy of the full terrain mesh for the ground collider, and the other mesh(s) for rendering the visible texture/geometry.
This is all so the player doesn't spin out unexpectedly on a seam.. Which it did, readily.. This is also a hack I'm employing on my main project until I code a better way.
I may try to merge the meshes together at run-time instead, but that might have to be a later update.
I remodeled the board itself, so you may find it catches here or there a little(lot) differently than it did before, had to get it down to a reasonable number of vertexes for instancing. And I think it almost adds a touch of chaos which is nice. You sometimes find yourself spinning when you didn't intend to, but it's reasonable and possibly more correct, for the physics anyhow.
What else... Just lots of texture shuffling, switching out shaders to the mobile versions and adjusting lighting settings until they are tolerable.
I converted ALL the text objects to TextMeshPro(just a free version) components as they manage to instance better than the default text objects do.
I made sure to replace all the Unity default sprite objects I could find(Background,Knob,etc..) as those can't get packed into an atlas, at least I don't know how to get them there... They cause all kinds of draw calls on their own. Just a few simple images.
Nearly EVERY quality setting in Unity has been set to the lowest it goes.
So... Does it run any better? v0.2.5: https://www.kongregate.com/games/WilliamOlyOlson/slingbot-boarding
I'm not entirely sure at this point, but I want to say yes... haha.
And here's 3am again.. Enjoy.
v0.2.7 out now, I fixed the colliders up a bit more, now using a mesh collider on the board for the way it moves across the ground as well as a capsule collider to keep it from getting stuck in things and spinning out extra-unreasonably.
Most of the builds prior to 0.2.5 I was using two capsule colliders to keep the board level and out of trouble. That seemed to contribute to some weirdness in collisions between player and NPC, something I still need to work on. A few other mesh/lighting tweaks/optimizations as well. Getting well into the 120fps range in the editor now. 
Also, the NPCs in this build are actually steering a few degrees at a time now instead of instantly rotating, which was causing a lot of bad looking behaviors. I still need to tweak it a bit because now they get lost/stuck on race courses a lot easier, so I need to put in some exceptions to the new rules here or there... anyhow.. back to it.
Enjoy!