It is worth it, but only to bump up the internal resolution and if you're happy with the speed games are running at now. Your HD4200 can only do 1 or 1.5x IR before it slows everything down. More importantly than that, your CPU is in need of an upgrade and is the real cause of your games running slow. You could do with a total system upgrade. i5-2500k's are very popular around here and work well.
Asus Laptop: K53TA
OS: Windows 7 Home Premium, 64-Bit - SP1
CPU: AMD Llano A6-3400M, Quad-Core, 1.4GHz-2.6GHz (Overclocked)
GPU: AMD Radeon HD6650M, 1GB GDDR3 (Catalyst 13.1)
RAM: Samsung 4GB DDR3-1333
OS: Windows 7 Home Premium, 64-Bit - SP1
CPU: AMD Llano A6-3400M, Quad-Core, 1.4GHz-2.6GHz (Overclocked)
GPU: AMD Radeon HD6650M, 1GB GDDR3 (Catalyst 13.1)
RAM: Samsung 4GB DDR3-1333