I have a 60D (so we aren't comparing apples to apples) and I went from the 50mm f/1.8 to the 50mm f/1.4. I like the 1.4, it does seem to be better build and doesn't feel like a toy. I always have a hood on the lens, so I don't worry about trauma to the AF system.
As far as the quality of my images... ehh... I think the f/1.8 is such a great performer for it's price and I always shot around 2.8 anyway. I don't think the 1.4 is that much better, but considering we are talking about lens prices, an additional $250 seems like a drop in the bucket considering the price of my 24-105 and the 70-200mm f/4 IS that I plan on eventually buying.
So the short answer is no, it isn't worth the upgrade in terms of amazing performance, but considering the difference in price which isn't really that much, I'd say get the f/1.4.
When I was buying golf equipment, I was willing to pay a premium for clubs that were top of the line because I didn't want to have the nagging suspicion that my drive could have gone 15 yards farther, or my wedge could have generated more backspin allowing me to be closer to the hole by an additional 3 feet. I'm a tad bit neurotic in that sense, so if you are a pixel peeper or you think that your shot could have been improved if only you had paid the small amount to get the better lens... then get the better lens.