Since the original 1000 has a W bracket, an I bracket isn't necessary since you can put a centered LNB in the 119 slot. Should be a bit more gain.
A little bit, but you have to remember, if you use a bracket designed for more than one sat location, it changes the amount of focal points on the dish. This defeats the purpose of the larger dish, as the gain is no different. Just like when you use a Y bracket on a 500 and one dual vs. an I bracket and one dual.
I went down this road with disappointing results a while back. Since 129 was sketchy on my 1000.2, I figured I would buy the W bracket and use only the center position to grab 129 (not realizing the gain would be no better). When I discovered the lack of improvement I started some trial and error to figure out why I was not seeing an improvement.
To make a long story short, I discovered that a D500 with I-bracket got better gain than a 1000.2 using the center position of the W bracket. Aside from the focal point issue mentioned above, I believe the fact that the 1000.2 is actually smaller than the D500 (on the vertical axis) contributed to the results.
So, my spare parts supply continues to grow as I slowly but surely purge my ignorance!