To except Splogs and make Adsense or not O My

Here is the situation had a Blog Multi network with Supporter and a Bunch of great plugins and themes from here about a year and 1/2 or so ago I took the site down about 10 months or so ago.
Two Months ago I decided to give it another go and used the Prosites plug in and activated pay to blog and gave them 30 days to try it and pay. I have been getting the people that just want the site to make a link factory to their sites. My first reaction is spam them and move on. So far no one has said anything because they know their wrong and got caught. But this post it not about how many splogs I'm getting. I have Anti-Slog active and Its great to stop the spammers and Bots with change the sign on feature. I was thinking about making the site Free with limited Plugins and Themes and paid users get it all. I did before and got a lot of link farmers.
This question if I finally get to it... Here it Comes.... Wait for it...... Wait for it.....
Should I just let the Link farm sites register and they get free sites for ever or until I put a stop to them. and I have my Adsense on their sites and ads for free blogs also.
OR
Leave it at 30 days free let the Link Farmers register and stay for the 30 days if they don't pay to upgrade have the Sign I did for Non Paying sites.
Let know know what you think. and What worked for you.