i'd guess that in the long run, primecoin will have a higher USD valuation than feathercoin (is that your definition of 'better'?)
USD price value of a coin would be the aggregate vote of all the market participants so i think yes.
that's true for overall market cap, but not per coin
imagine a cryptocurrency almost identical to bitcoin, except there will only ever be 7 of them created. these "stupidheadcoins" might be worth $1000 each giving the impression of a valuable currency, but they are clearly not a better currency than bitcoin overall
USD price per coin is only relevant in the context of how many coins there are / will ever be, and with primecoin there's no hard limit