My desktop has AMD 3400+ on an Asus KV8SE Deluxe mobo - pretty old now. Mine has AGP slot, so may be similar to yours?
If so, I recently installed a Sapphire HD3850 AGP 512Mb card, and it has improved things dramatically, and extended the life of the old machine. My old card would not run anything requiring shader 3.0, so became useless as far as newer game titles were concerned.
So I would say yes worth upgrading, but there are limitations on the number of AGP cards these days. I think u might need at least 400w PSU too. Hope this helps.