This class just doesnt seem to die with the feedback, which is nice for polish . Now back to the issues that Mr. Giant has with this class:

I dig this. I very much dig this... apart from, oh, the last three levels.
Yeeeey.....Oh.....

Aura of Mundanety comes out of no-where, and doesn't seem to have anything to do with improvising. How are you projecting an (Ex) antimagic field? Why are you projecting and (Ex) antimagic field? It's like I've suddenly wandered into a completely different class.
This class feature was a bit of a mindspin, I'll admit that. Also, it does not capture the feel of the class entirely. However, back then (and even now) I cannot think of a class feature that is
1. Interesting,
2. Powerfull enough to keep this at tier 3
and 3. Is Ex, because that is one of the main design points I had with this class.
Do you have any other ideas, please let me know.

Skill Trick Mastery should probably have been handed out levels ago, back when skill tricks were still useful.
Got a point there, I'll shift it down a few levels. However, I would need to brainstorm about a replacement before doing that (Dead levels are not nice).

Ultimate Improvisation, again, comes out of no-where, although I do at least see the idea behind this one. But... well, a lot of the spells you list are... silly. "Hold on, let me just glue together these toothpicks and this tin can and voila! Power Word Kill!" If you want something like this, I'd start handing it out sooner, and take a really good look at the spell options you allow.
I do not agree on this one though, you can emulate low level spells with your Improvisational Tricks quite early (Think, Shatter, Mage Armor and Fireball for example). As such, I think this is a fitting capstone for the class. On another note, you need to prepare the stuff beforehand, so it is more like: "Give me half an hour guys, I can make some makeshift rockets and hey, Meteor Swarm." Nevertheless, I should probebly mention that the spells don't look the same as their magic counterparts (its improvised after all)

All in all, thank you for your PEACH, it was really useful to correct a few points of the class.
If you (or anyone else that reads this for that matter) have any ideas on what to replace Aura of Mundanity and Skill Trick Mastery with, I would gladly hear it.

Cheerio,

Way