Siegecraft is certainly a useful technology. Not only do you have extremely cheap tower and wall killers, you also have the element of surprise at your side. However, against most military units villagers still suck. However, due to the low cost of these units you can spend more on expensive units like heavy cavalry to guard your villagers hacking away at enemy towers and kill enemies.
Jihad is a dangerous technology. By researching it, you get extremely cheap fighters and in combination with expensive units and the siegecraft technology these can be deadly. However, the drawback is imense. If you for whatever reason don't succeed with your attack, you basically have lost because you can hardly gather anymore resources.
In some situations it may be worth trying it, but I would reccommend using it only when you're sure your attack will succeed.
Maybe a moderator can move this to the Age of Empires/Rise of Rome forum? I'm sure the forumers there can give a lot better advise about RM and DM tactics than scenario designers. I have never really tried a villie strategy (except in some scenarios), so I'm not speaking from any experience, these are just theories.
While sausages are tasty, you might cut your finger with that pencil over there.