I've never seen a minimum bid of $.75 or $1.50. It seems odd that you go from $.50 to $1 to $5.
It would be much more helpful if there were $.10 increments up to $1 and $.50 increments up to $5.
We have a small, but significant number of keywords where the minimum bid is $1. These keywords convert well and are relevant, but we don't have the resources to create tons of seperate landing pages so the QS does suffer a bit. In many cases, $1 is a bit too high, but $.70 or $.80 would work quite well.
The same applies to $5 keywords on occasion. There are times we could bid $1.50 or $2, but this is rarely possible for keywords with minimums that jump from $1 right to $5.
Also, I've found that ads using {Keyword: Alt Title} in the title text do better since it places the keywords in the title.
I'm more surprised that Google's sophisticated system doesn't have more complex gradients for minimum bids. Going from $.50 to $1.00 to $5.00 with no steps in between seems a rather blunt way to address this problem.
Maybe I'll add this to the 'things I'd like to see' queue.