[alexpigment]

Is there any other advantage for GPU rendering beside a lower CPU usage?

In answer to your question, decoding the video on the GPU is really the main advantage. But it's not as simple as "render on hardware A as opposed to hardware B". GPUs specifically have the instructions in them to decode H.264 videos and CPUs do not. Therefore your CPU is having to work much harder to do the same thing that the GPU is doing. Imagine the difference of running Windows in a virtual machine (CPU) vs. running Windows natively from an installation (GPU). Luckily, you have an i3 chip which can probably do HD H.264 (I don't know from experience) on the CPU cores alone, but if you're on a budget-level or atom CPU, HD is not going to happen.

Also, if/when budget is no longer an issue, there are lots of low-profile nvidia cards on the market for very reasonable prices. See http://www.newegg.com . Haven't checked in a while, but I'm sure you could get what you need for $50 USD or less.

UPDATE:

HERE is a quick newegg search on Nvidia cards that are low-profile-ready and have an HDMI port on them. Just ignore anything from the 8000 series and you should be good to go: