The difference between 26 and 29 is only small, the difference you may feel going to 650 will be even less.
I wouldnt bother, if you want to go faster the cheapest and by far the most effective way is just to get fitter.
Dont get suckered into marketing hype, or looking at others and thinking it must be the bike.
Well if you are not a racer then I'd largely agree with you. The difference between 26/650/29 is noticeable and there is a significant difference in my opinion. Agreed about getting fitter, but that only uphill and I think the biggest benefit of larger wheels is downhill.
Finally, its not about marketing. I think that is something that you would find out for yourself should you ever ride a 650/29 bike.