Right, that's what I'm thinking - "something useless that tries to grab your attention and steal some of your time."
I'm thinking of spam in terms of email marketing. I think with Steemit, since the only way you can send a memo is to literally provide value to them, the grey area is even more grey.
I really think that if they follow you then a memo is completely warranted. If the recipient isn't a follower, they're still receiving value and shouldn't have a problem with it as long as your memo is genuine and helpful. Back in the old days companies would send out physical mail to cold (new) prospects with a dollar bill inside to increase their conversion rates.
email marketing is still to this day the most effective way to build up relationships with people that have interest in a niche. When you buy from ebay you will get sent emails from ebay about related products that you have looked at. I use email marketing massively but its in exchange for value that I share and its through an opt in page so the recipient has consented before hand. I started an email campaign to bring in new steemians which also helps me to automate emails giving them guidance on how to get started. Here I would say if people have opted to follow you they can always choose to unfollow just make that option a clear choice @money-dreamer clear at the bottom of your memo and if you are interested in starting an email campaign come and have a chat with me. You could even put a caption page link in and build a list of subscribers and that way it does not matter what platform you are on your list is yours to update when ever you want. like I am about to shoot a quick email to my list to invite them over here to steemit. Anyway cut a long story short if you point out that people can freely unfollow if they feel offended then at least you made the choice clear and that's fair in my books :)