Round cables do increase airflow, but weather they are worth it or not depends largely on the price. If you can get hold of them cheaply enough then go for it they not only increase airflow but they look better too, especially if you have a window and Cathode, and you get the UV reactive ones. Personally I still use the ribbon cables I see no need in upgrading to round cables yet, my standard ribbon cables dont restrict much airflow because they are taped to the side neatly out of the way. Also standard ribbon cables can in some cases be more airodynamic than rounded cables because they are much thinner, to accomplish it though you need to fold them out of the way of the direction of airflow witch can be a little tricky. The only time i would use round cables is when my ribbon cables break and need replacing or if I was using a window.
As for those syetm blowers, it might feel like it when you put your hand behind it but they dont shift much air at all, there alright if you put them under a graphics card to hirt a bit of the hot air away from the card but they dont do that much. Having said that i used to have one in the slot above my graphics card witch meant it could pull a bit of the heat away from the heatsink, and it did actually make a fair bit of a difference, athough not many motherboard position the AGP slot to allow for a free space above it.
