AMD's new HD 4550 is a great evolutionary step up from the HD 3450. The 3D performance has greatly increased, yet this is definitely not a gamer's card. While you can certainly play most games at modest resolutions with some eye candy, many people have just gotten used to turning up everything to the max to match what they see on marketing and review screenshots. If you are just looking for something that plays better than your integrated graphics, the HD 4550 may be for you. On the other hand, for a few extra bucks you can get a HD 4670 or 9600 GT which offer much more performance per dollar.
The media playback features, compared to the HD 3450, have also made a step forward, but there is nothing revolutionary. UVD 2 now offers decode acceleration for a second HD video stream which is often used for director's comments in special editions. On previous generation products this decode was done on the CPU, now it is done in hardware. But since the secondary stream is running at a lower bitrate and resolution it wouldn't tax your CPU that much anyway. Another area where incremental improvements have been made is the HDMI Audio feature. On the HD 3000 Series you could go up to 5.1 audio over the HDMI link, now 7.1 is supported. But obviously your decoder and speaker setup needs to support that as well on the output side. If you are building a media PC on the tightest possible budget, the HD 3450 would still your weapon of choice.
Where this card really shines is its completely passive cooling design making it a noiseless experience which is crucial in any home theater setup. Also I would like to mention the extremely low power consumption and overclocking potential of this card. While they are only of secondary concern for you as the end user, they show how well AMD did their job engineering an efficient GPU that runs well without drawing loads of power.