I have two machine I am thinking about upgrade
My good machine has about 3 exhaust fans 2 intake fans. All of these fans do about 50 cfm they also about 3.5 years that machine on 24 x 7 which mean they are at about 31000 hrs of operation. None have any problems as of yet ,but uasally fans life is about 25000 hrs operation. I can upgrade the older machine video card ,but then can't replace the fans. I am do other uprade to. I am thinking of gooinf from ati 7200 (on hardware rending) 6200 nvidia.
If don't do the video card I can afford to buy four new fans which run about 90 cfm each greatl improve the cooler plus don't have to worry that my fans are well beyond their liife expentcy. The other if buy these fans I am going to take one the old ones and mount it so blow air across the ram. Helping the ram to ran cooler. Cooler system live longer and have less carshes, not that this is problem right now. My system current at idle system temp is at 82 f and cpu temp is 97 F. At full load runs 87f and 107f. Cpu fan at about 40 % speed. Have thorttle up I have set to 115.

Go for the fans, you dont want to spend on a new vid card and then suddently have your whole system toast and have to plop more money than the vid card because the fans died. Ive had only a couple of fans go bad but I had advanced warning that the cpu was overheating so I had time to shut er' down and get a replacement.

Also unless you do some overnight filesharing, I reccomend you shut down your computer every night. Saves energy, almost doubles the life expectancy of the components because they are not running during the other half of the day while you are sleeping, ect. I do so on many different computers over the last decade and experienced no ills because of that, theres really no reason for the computer to be on overnight unless you are dl or doing maintinence like defrag, virus scan ect.

I saw go for a new case..I need one, 80mm fans did not do much so I just have my covers off the side...runs more stable than ever before. I am not OCing it that much though..I also need to go AMD...

Lately my system been doing about dvd buring. So it spend lot time at full load. The acutal it isn't really how lot ware keeping system up all the time. Most hd have life expantcy of 20-30 years nonstop opreationd And well cicruit don't really wear out. And your system use the most power at startup I know mine from battery back with montor use about 380 at start up. And full up use between 260-280 . Have the hd set that if they aren't in use the go offline. And I do oprate all flat screen for montiors all 4 of them they set at 5 mins when they shut down which saveabout 30 w