It would be cool if there was a betting script where you could chose the betting logic (martingale, random, reverse martingale, whatever) and the site (coinroll, satoshidice, primedice, etc) at run time.
If each betting strategy and each site was separated out into separate functions then it would be relatively easy to add new sites, and new strategies, without having to reinvent the wheel each time.
The only thing that puts me off is that running a bot against sites with negative expectation is kind of a silly thing to do, and writing such a bot could make it look as if you were encouraging people to partake in such silly activities.
I think the biggest problem is that there is no general protocol these sites use for their various functions. Coinroll.it does it the best from what I've seen. They deliver account creation, deposit, withdrawal, and betting functions with output in an easy to use json format. Other sites may require people to parse the sites response for things like a deposit address. Not hard to do for an individual site, but certainly annoying for multiple sites.
I think a decent approach to this would be utilizing a language that supports interfaces like C#. We could design a communication interface that handles actually sending information to the site, meaning things like withdraw and bet, and a logic interface that determines how much to bet and when to withdraw. Implementation would be an exercise for the user or general community.
If there's interest I could write that up fairly quickly with a coinroll.it example.