I obviously can't advocate spam, no matter how you try to justify it, its still spam. However. I personally regard SPAM as the following.
An entity that continues to email me more than once during a day and every week or more.
An entity that even after unsubscribing sends me emails.
An entity that sends me completely irrelevant things e.g ***** Extensions.
If I were to receive an email, and I have, which is targeted to my field and could actually be interesting to me, does not look like spam or trying to sell me something I will either look at it, check it our 1st or I will just delete the email, if they send it again, I will unsubscribe or continue to delete, if sent again I will respond with an unsubscribe.
Sending 50 emails aint really going to cause you or anyone any problems especially if targetted and I doubt these 50 people will report you. If you kept hounding them it would be different.
Personally I think it's a difficult area, although it's not and it's very clear.
If I had a genuine cure for some disease which people were inflicted with, would they be annoyed/report me if I dropped them an email...Is that still classed as SPAM???