I reckon the amount of money being spent punting by forum readers is fairly constant on average.
So the spamming advertisers are trying to increase their share from us.
Each of them will try to do this in their own way, using one or more techiniques, Eg:
- provide up to date roster info
- give good info about their girls: size, dimensions, services, etc
- provide pictures
- encourage punters to write reports
- spam
- others ...

Spamming appears to be the low cost shortcut way to try to increase market share, since you are not really adding any value or doing any "work" as such.
But does it work ?

I think once a punter has frequented a place a few times they will form an opinion about whether that place is worth visiting for various reasons:
- easy to contact and organise a time/lady
- keeping bookings
- truthfullness of info and pictures
- quality of ladies
- services actually offered
- value for money
- location
- others ...

I think most/all of us repeat punters ignore the spam as best we can and dont' even read it, so it's pointless in the main.
I think spam may only work to attract interest from first time customers to a shop, however the more savy potential punters will be
looking at the rosters and girl details and then reading any real AR's and base their decision on this.
If spam does attract interest then the points above about increasing market share come into play.
The only reason I can see spam working then is to attract mug punters.

If I was running a shop I would provide rolling daily updates to my roster thread, in the roster section looking forward a few days, and also details/pictures of the girls etc, either via weblink or in the actual post. (Via a weblink would be better as it's not just forum readers who will potentially see it). I would provide quality girls at a good price and then I would expect good ARs.

If I had low quality girls and was not offering good value then I would rely on spamming to get a constant stream of first timers to my shop.
So if a shop had high quality girls and offered good value it doesn't make sense to spam, it won't increase business, it is actually bad for business because you will annoy people.