[Election-Methods] Measuring power in a multi winner election

[Howard Swerdfeger]

I know that this list is primarily single winner elections but I thought 
  given the low volume as of late a slight change of topic would be welcome.

with that, I was wondering about multi winner elections. specifically 
the  parliamentary kind typical of most former British colonies.

Do to the inadequacies of the FPTP system in creating a government many 
of these countries are looking at alternative systems, New Zealand moved 
to MMP, Scotland as well, BC tried to once, and will try again move to 
STV, Ontario is looking at MMP.

The drive behind thes moves it usually that the old system fails to 
translate votes into seats "fairly". (Votes != Seats)

but most of these reforms fail to recognize that that Seats do not equal 
power. So we are still still stuck with a similar problem (votes != power)

I was looking into 2 methods of measuring power in a weighted voting system.

http://en.wikipedia.org/wiki/Banzhaf_Power_Index
http://en.wikipedia.org/wiki/Shapley-Shubik_power_index

I was wondering first if there are any methods of measuring power in a 
legislature that I am unaware of? Secondly if anybody has tried to 
design a generic system where by votes are kept proportional to power, 
via allocation of seats?