I agree with your point that a person who does not trust presently available cryonics should still invest in research. However, it does not necessarily follow that the optimal expenditure of a given dollar from any source is on research. A person may have a high enough estimate of the probability of it working adequately for it to be more worthwhile to purchase an existing cryopreservation than donate to research.

Or they may think research has hit a point of diminishing returns which cannot progress further until mature nanotech is available. Alternately, cryonics could be rendered very inexpensive (by economies of scale, e.g.) such that more value is gained by each additional cryopreservation than by equivalent donations to research. A philanthropist such as Larry King might, after all, consider offering money to cover the freezing of millions of low-income individuals in high population countries. The simple act of doing it millions of times under a variety of conditions could cause drastic increases in quality.

Furthermore, note that research itself can be supported by sale of the results rather than donation alone -- e.g. from what I understand cryonics is a large part of the market for the M-22 cryoprotectant, something which represents a large portion of the cost of an Alcor cryopreservation. If it is simply easier to get people to spend money on cryopreservations than research, it could be a more effective source of revenue. If there is competition amongst cryonics companies (or strong internal pressure) to provide the best possible service, a thriving market for cryonics could be the quickest route to developing an adequate product.

Another thing to take into account is that each additional cryopreservation means putting more money into a trust fund to keep things going, and to eventually fund reanimation research. Since reanimation research will tend to involve brain repairs, this effectively represents a delayed, interest-compounded donation towards brain trauma reversal science -- perhaps scanning will be what works, but we can expect other areas such as direct repair strategies to be investigated. So there is a certain amount of additional value that has nothing to do with cryonics itself. (Economists may be able to comment on the value of long-term trusts, which I understand to be stabilizing for the economy as it concentrates money in low-risk ventures.)

The only examples of cryonics companies having to let their patients thaw that I am aware of involved the flawed pay-as-you-go business model, which is no longer employed by cryonics companies. Instead of collecting monthly payments from relatives as the practice was, advance payment of a certain minimum is required, which is placed in a trust fund to earn interest over time and thus cover the patient's expenses indefinitely. No cryonics company using this business model has yet failed catastrophically.