If humankind survives long enough for upload/immortality to become possible, then the living people of that time, or the recently dead, will do equally or better for the task than long frozen corpses. Yes the technology may quickly develop and be able to upload frozen brains, but it is not required.
I do not agree with calculations linearly summing the worth of immortal beings. My guess is that the return will quickly saturates: once you have a being that is willing and capable to improves itself, no more uploads are required. The immortal being can acquire diversity in other ways, and may create diversity too (you don't need a human body to do that). The amount of redundancy in two humans is incredibly high compared to the possibilities in being-space.
Would it have no cost to me and humankind, I would sign up. But given the resources required, I don't think anyone should do it (in the same way that I don't think anyone should drive a Hummer in a city).
I deem that I have other means of becoming "immortal" that are more efficient (yes, including "having kids and transferring them part of my values/knowledge"). My take is that intelligent people should spend their energy trying to convince the population to minimize existential risks, not to sign up for cryonics.
Yes, if large economy of scales changes the situation before I die, I may change my mind.
Here are some points that may help identify the source of the disagreement.
For a given amount of resources, the benefits of cryonics have (among other things) to be compared to the benefits of increasing the probability to reach the technological level enabling the upload (i.e. before extinction of the specie).
The utility of uploading 10^10 people is not 10 times greater than the one of uploading 10^9 people.
If part of a transhuman being to which I have not been uploaded happens to turn out as I would have myself, then I am already there.