About the general problemThis is an interesting and important question. In the most extreme theoretical cases it could even have radical implications. If the differences in magnitudes of expected utility from donating to a cause and eating vegan oneself (including talking to others about it, being a role model, etc) are big enough it could even be justified to go on eating meat. There is always some cost (initial or continous), in time, money or willpower to making a change in one's life. The crucial factors here (except the utility comparision) one's ability to divert different types of resources to different ends.
The specific question: Private consumption among utilitariansSpindoctor, I agree with your original reasoning, DanieLC and RyanCarey. At least for someone who is a member of the utilitarian minority it seems better to spend the money on an effective cause like Vegan Outreach, rather than on more costsome cheese-substitutes. Of course, as has been pointed out, this assumes the money won't be spent in some non-utilitarian way.
One way to ensure that the money is spent the right way would be to keep a strict budget, including categories like food, necessities, utilitarian causes, and fun. With such a budget the cheese choice would manifest itself as the question whether resources should be moved from the utilitarian category to the food category or not. Such a strict budget could also help to avoid the risk of a slippery slope.
RhetoricsOn the other hand, a (reluctantly?) converted vegan mightn't be as persuasive as Spindoctor.
Probably only a small fraction of one's persuasiveness depends on whether one eats vegan cheese or not. And with out good evidence we cannot even sure if not eating vegan cheese will make a positive or negative contribution to one's persuasiveness. Strictness might persuade some, but it may also frighten others. To know which effect is bigger we need quantitative data.
Effectiveness of vegan outreach?The question here shouldn't be whether VO is more effective, but whether there is *any* utilitarian cause that is more cost-effective (for example, investing in
in-vitro meat research). This also includes the alternative of investing (link?) the money and waiting for knowledge about what the best cause would be while letting the money grow. So to be the favoured utilitarian alternative spending money on veganism for oneself would have to trump all possible ways of spending money for the rest of one's (utilitarian) lifetime.
In fact, after looking at some statistics of veganism and vegetarianism I'd say that the future looks pretty bleak if it really would be the case that changing private consumption would be the best way of using utilitarian resources. That is, from the statistics I've seen it seems like the increase of veganism/vegetarianism has been small if not non-existent
the last 15 years. Furthermore, in the same time meat-consumption in the world has
increased radically.