Have you had success improving your Google Adwords impression share?

We haven’t.

We’ve followed the guidelines and implemented their optimization suggestions and still our impression share is at 43%.
According to Google our losses are due to “Rank” not budget.
We are using 300+ negative keywords to weed out any irrelevant search queries and our campaigns are made up of 12 to 40 adgroups each focused on 1 or 2 keywords.
Our other stats in general seem good; Avg. position 1.5, a 2.5% CTR and a 3% conversion rate.
Our goal is 100% impression share, or very close to it, so how do we achieve this?

Questions:

1. Is Google’s impression share a reliable metric?
2. What is considered a good impression share?
3. What activities should you focus on to improve impression share?
4. Does Google provide you with vague unclear answers when discussing impression share?

*Other KPI’s such as CTR, Conversions and Cost Per Conversion are just as important if not more important than impression share but our goal/focus at this time is to see improvements with our impression share.

Our daily budget is more than half the amount we currently spend.

Look forward to reading your comments.
Thanks for your time.