I think those might be a bit too arbitrary, not to say they aren't good starts. Whether something is a SPAM or not requires a bit of assessment. Consider the following:

www.buymygold.spam.com 10,000 gil $50
www.buymygold.spam.com 10,000 gil $50
www.buymygold.spam.com 10,000 gil $50
www.buymygold.spam.com 10,000 gil $50

vs

DPS LF Fate Group
DPS LF Fate Group
DPS LF Fate Group
DPS LF Fate Group

I dare say different people will assess it differently. For as long as something requiring human assessment, it cannot be automated fully or something will go wrong in its execution.

Seeing how much time and effort they have to spent responding to harassment report and forum post, a better use of their time might be to setup a monitoring task force. No, not to have them pop in and out of each city each zone, that would be very wasteful. Meet them half way mechanically by providing them monitoring alerts. Something to what the degree of what you said above, say, 30 shouts within a minute or two. Raise an alert, the enforcement team picks it up, assess the shorts, enforce, done, next.

Since every chat is a client to server and server to client broadcast, it is already being processed by the chat processor code. Added some sort of rolling real time tally is trivial, storing the chats can be costly (both in terms of processing time and write time) but necessary for enforcement, if the data is indexed correctly, any sort of data analytics tool can highlight potential spammer. The rest becomes policy enforcement.

Right now, the worst thing SE can do is try to think of something too smart before they know how to handle the problem. Have to walk before running. Low impact (on game speed), high accuracy (human assessment), efficient (mechanically assisted) mechanism is the first step.

Just my 2 cents.