If marketing expenses don't have a positive return then it shouldn't be done at all. Funds should only be used if it would actually have a positive effect on value
When we decide on how much money to use for marketing expenses, we need to realize that there is two option you will get.
First, you can get success with your marketing strategy and the second, and you can get fail because your marketing strategy is not good enough to explain to the public.
So you need to make a great marketing strategy to reach your goals, you can fill what people needs, and besides that, you want to introduce your project to them so you can get a huge investor and customer. I see the ICO marketing was almost the same for each project, and I think if one project fails, soon the other will fail too because people will think that the project has run by the same people or teams.