Likewise, I am in the same boat, but have a little different situation. I'd been wanting the 50 1.4 for a while, but didn't want to pay full price for it. Then the 40mm pancake came along last month before Thanksgiving and with the $50 instant saving, I bought it. Since that time, the prices on the 50 1.4 and 1.8 have come down. For the build quality, I would go for the 1.4, but since I have the 40mm, I can't justify buying a 50mm for double the price of the 40mm. Two lenses with 10 mm focal length apart. If I didn't have the 40mm, it's a no-brainer that I would go with the 1.4 and be done with.
Still not sure what to do, but I might just keep the 40mm. Either way, can't go wrong with either one. You can't beat the current deal though.