46C is absolutely fine - quite good really.
What is the cooling on the case at the moment? Is there an exhaust fan? If not then rather then getting in intake, get an exhaust, as these are more effiecient at moving air through the case (rather than just blowing it about inside). You could get two akasa ambers for intake and exhaust if you wanted and remain equally as silent.
As for the RAM... it largely depends on the RAM you have at the moment. If you have 2 x 512Mb, then I wouldn't get another lot, as the board won't be able to run the RAM at 1T. In this situation, I'd wait till you have enough money to buy 2 x 1Gb and sell the stuff you have at the moment. If you've only got one stick, then go for another single to get you to 2Gb