Is there any point attempting to vote when my hash power is so marginal? With regards to /P2SH/, is there even much point in voting with 500MHash or so of hashing power given that the chances of finding a block within the voting timeframe is incredibly slim? Not to mention that my vote will be shadowed out by miners with larger operations.

Is the voting system unfair in this sense? Or if I want my vote to count for more should I just be piling on more MHash to show a greater support of the network? (as in, people with more MHash are entitled to more votes because they help support the network more than I do?)
You can still vote by supporting a pool voting in the same way as you.

Voting is rather fair, as bigger pool operators have a bigger responsibility to their miners to keep the software up to date and operating according to their best interest. Thus mining in a pool is like voting for your representatives - you give your trust to them so they can work on benefiting you.