I can only speak for myself here , We set up a domain just for adwords adn the mailing list , we spend about $3000 a month and it is worthwhile for us.We use adwords for certain poker terms only and in this google acct we have only 1 domain , we dont use adwords on the same google user acct that we have gambling websites.
Obviously when you do as we do using just a email list form and not having any linsk to click the risk is higher and conversions lower than having a website with all the links but we have found it worthwhile .Google.co.uk is where we have ads , same ads were declined on .com and .ca.