If anyone is interested in aggregate returns, several years ago I recorded the stocks which were spammed to me by e-mail for a few week period of time. There were around twenty of them. Tracking them showed that on average they lost about half of their value after around a month and a half after they were spammed.
I also looked at the trading before they were spammed but there wasn't any clear direction there. I expected a slight bias upwards before the stocks were spammed but the sample didn't show that. The prices were fairly random up until that point. My guess is that either most spam is unsuccessful at making the spammers any money or that the spam takes place before someone holding the stock decides they want out. At any rate, the odds seem heavily stacked against anyone who actually buys a stock which was spammed to them.
A couple of years after that, I was going to record and analyze another round with a bigger sample but never got around to analyzing it. I'll paste them here in case anyone wants to try--although generally tickers and names change often at this level so it might be hard after this long. But just in case:
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