Did you know that only about 5%-10% of seats change hands between boundary reviews? The biggest 'change' elections (1945, 1966, 1983, 1997, 2010) happen after a major boundary review (even then only around 20% of seats tend to change hands). It took nearly 70% of voters to vote against the Conservatives in 1997 to finally remove them from power after 18 long years, and over 70% of voters to remove Labour after 13 years in power.
It has become clear to me that whoever draws the boundaries has more power than the actual voters under our present system. This is why first-past-the-post is only semi-democratic.
Proportional systems remove the importance of boundary reviews because the proportionality and fairness of the result are assured. PR also ensures more representation for lower socio-economic groups, minorities, women and higher turnout.
Finally the more proportionally elected countries enjoy more equality, prosperity, better public services, less corruption and higher political engagement measured on any index you care to mention. Go and check it out. I think for these reasons, the case for change to a more proportional system is undeniable.