The net result, is most any given man is going to see more success in getting responses - and dates - by spamming any woman within a hundred miles than by writing the kind of message women publicly opine to want.
This comes across as cynical towards the women on dating sites. The problem is that the women on dating site become a lightning rod for messages. If every message were of a kind that interested a particular woman, how would she respond to (e.g.) 10-20 messages from new people every day? She's likely not going to end up going on dates with multiple people at a time, and if she finds someone long-term, it's (more than likely) only going to be a single person. She likely will only be able to carry on a few meaningful conversations at a time, and the rest just get dropped. If she were trying to meaningfully respond to everyone then going on a dating site would end up being a significant chore.
Edit: Also, it's probably difficult to respond to someone that puts in the time to right a well-thought-out message, but doesn't come across as interesting (or expresses views that are contrary to your own -- e.g. an avid hunter messaging an animal rights activist). You don't necessarily want to be the bearer of bad news, so it's easier to not do it at all (or you convince yourself that you'll respond 'later' but 'later' never happens).
Real success is extremely hard to quantify, which is why i'm not suggesting that as the goal. The goal is to grade spam messages, and encourage people to not repeat known spam patterns. (And, if you show the score to the recipients, it also acts as a spam filter.)
Encouraging / forcing people to write less spammy messages might improve the overall message quality, just by increasing the cost, in effort and time, of sending the messages. It also provides some minimum level of feedback to the people who get zero responses from their messages.
IIRC, when the user disables/deletes his/hers OkC account, they can specify the reason: "met someone on OkC (they can type the other person username)", "met someone elsewhere", "not interested anymore", etc. So they probably have lots of good data on success.
Self-reporting in general is fraught with problems, doubly (quadruply) so when it's something as close to the ego as dating.
Also assuming the account is shut off at all as opposed to simply idled.
lol
-Message that are too short get banned.
-Men that are frustrated should now that being funny and referencing something in their profile, or talking about something they both like are good conversation starters. Just as they are in real life.
-Sexual propositions is good, you can ban them or not, at least you know exactly what they want. They are bring honest.
-Send dick pics gets you banned.
This leaves you with a good set of people. The next step would be for the system to learn what the user wants, and start to filter these messages.
- Messages that are too short. E.g. "hey babe" doesn't mean much, when a women gets 10 - 20 "hey babe" messages in a day.
- There are men that get frustrated at the lack of response from women, and start turning their messages into "form letters" which don't show any level of having read the woman's profile.
- Initiating conversation with sexual propositions.
- Depending on the platform, sending unsolicited pictures of genitalia.
While some of these might not qualify as "spam" compared to a 419 scammers emails, I would say that wading through all of that seems akin to wading through one's spam folder...