However, because the way they measured it pushed the limits of engineering, if GP-B had NOT agreed with GR there is good chance the results would have been dismissed as most likely due to equipment flaws.
While it is in general a good idea to confirm measurements, especially using different techniques, in a case like this where the confirmation will be much less precise than the other experiments and will likely be rejected if it fails to confirm, you have to wonder why this was funded over other projects.
The answer to that turns out to be simple: politics. When space scientists ranked all the proposed missions under consideration, GP-B came in dead last. However, its proponents went to Congress, and got Congress to override the normal process for prioritizing missions, forcing NASA to move it to the front, ahead of more scientifically worthy missions.
There are a lot of very worthwhile scientific missions that we can't fly due to budget limitations. It's a shame to see $750 million of the limited budget go to a mission so far down on the importance list.
Also I'd be interested in sources, as well as genuinely curious what missions would be more important.
Here is the stack rank of operating missions as of 2008 (when NASA needed to shut down some missions to save money):
1. Swift, 2004
2. Chandra, 1999
3. Galex (Galaxy Evolution Explorer, ultraviolet), 2003
4. Suzaku (X-ray), 2005
5. Spitzer, 2003
6. WMAP (Wilkinson Microwave Anisotropy Probe), 2001
7. XMM-Newton (X-ray Multi-Mirror Mission), 1999
8. Integral (INTErnational Gamma-Ray Astrophysics Laboratory), 2002
9. Rossi X-ray Timing Explorer, 1995
10. Gravity Probe B, 2004
I also found this read (http://www.skyandtelescope.com/news/121390204.html) very interesting.
So, sure - the proof may not be epic -- but the prediction certainly is, especially even moreso that he is correct (again)
He developed mathematical models for currently available observations. Those models in turn also suggested other phenomenon that could not be measured at the time. As time went on, some of these have been measured and found to hold true, others observations about the universe have been had that suggest they don't hold true in all cases (eg: "dark" stuff)