Its a difficult decision you face. You are not the first person on AVS Forum to complain of getting a defective replacement unit from Epson. Part of the reason is that a replacement unit could be and likely is a refurbished one to start with. Some have received great replacement units while others have complained of going through multiples to get a good one. I can only assume a certain number are received back by Epson and the tech classifies it as "no trouble found" and it's boxed up and sent back out the door to replace a defective one.
I am an onwer of an 8700UB so much of what I have stated is based on what I've read in the 8700 owners thread and my personal experiences. I absolutely love having the picture quality of the 8700 but I question the reliability of them based on my own experiences and reading the experiences of other Epson owners. Based on my own experience and what I've read my Epson 8700 is the least reliable piece of equipment I've ever had in my home theater. My 8700 is a month and half out of warranty and has only 450 hours on the bulb and has started to develop color banding in some areas of the image.
Some of the issues with projectors are due to the nature of the product... a projector lamp is a consumable item and it's performance changes over time but that only accounts for a certain percentage of the problems that owners have. For the most part I think people are aware of lamp life issues prior to the purchase.
The difficult thing to determine is if a projector from another manufacturer is going to be any more reliable or if they are going to have better warranty service. In some cases probably not, for instance if you bought a projector from another manufacturer that was made with Epson LCD panels then you are prone to experience some of the same problems.
If I were in your shoes I would be calling Epson and requesting another replacement unit and doing so until I received one I was happy with. Hopefully your next is one is better.
Price is what you pay. Value is what you get.