Even if you have a domain that has been at Fabulous (or any other PPC service for that matter), you will not know how big the clicks will be. You can check the values at Overture to get an idea. I can have a domain at Fab earning $.10 per click consistently day after day and then bam, I get a $3.00 click. There are so many variables. The best you can do is study your results to figure out which domains earn the highest average rpm, or better go by average income/day. Use that to help guide you towards your next purchases.
I do not pay a lot of attention to $/click, as I have found that I can end up with domains with no traffic! It is the combination of traffic and rpm that multiplies for your bottom line.
For example, "personal injury lawyer" might show up at OT as $10/click. So, I think wow, there must be lots of related domains. I try registering a few, and they are total duds. Live and learn.