We were told about the same from Wineguad, that we would have to have a new dish to get HD. We decided to go with a ground mount for several personal reasons.
After using the ground mount, (with Dish Net) the only problem is/was that we had to run new cables to eliminate the splitters DRV have in line on the factory install.
We have had HD for over a year and the other day, I decided to check out the roof mounted dome dish and ran a coax direct from the dish to the DVR receiver. After running the setup on the receiver, the dish found the satellite and locked on. I then went through all of our 250 channels and when I switched to another channel, the dish would switch to the proper satellite and lock on. I could not detect any loss of sharpness in the picture.
Before you replace the dish, you might want to run a cable direct to your receiver and try it. The only thing I had to do was remove the cover and change the dip switches to change from Direct to Dish.
Dish service advised they can not use a splitter before the receiver, only after. Direct can use splitters before or after the receiver which is the reason to use a direct cable for testing. The down side is that you will only have one input to your receiver which is not a problem unless you want to use a DVR and record another channel while watching a different one.