I think you just have to view at it like paid advertisement.

If you have a good product to offer, the cost will be definitely worth it in the long run since people will get to know you and your product. And if it is good, they will use it.
However if you are just promoting garbage people most likely will not follow you or in the even worse case even downvote you for promoting spam.

Just like I for example would like to do with the "XXXLutz" advertisement in Austrias TV - cause it is just so annoying!