Well, it kinda depends on what pretender you're going with. I seldom go below a 7 on dominion, but where to go above that? Depends on how many points I have left over after getting the paths I want for blessing, and also if I want a SC god (to get the awe at 9 or 10).
The levels above 7 are generally pretty expensive so you've got to balance them against what you could have for the same points. Having 30% more jaguar warriors is nice, but is it worth the price to go from 7 to 10? Well, there are a couple ways to go. I like to get 2 extra castles up as fast as possible, and 30 jaguar warriors a turn is a pretty potent rushing force with a decent bless. But if the other choice is to have an awake pretender to back up 21 jaguar warriors a turn? Or a second bless for those 21 jaguar warriors? On the other hand, if your choice is to move your dominion from 7 to 10, or to move one of your imprisoned pretender's magic path from 4 to 7, or drop sloth from 3 to 1...well you've got to decide where the best bang for your buck is. I seldom plan to try and dominion push when I'm building my pretender, but if I end up with a 10 for other reasons I'm much more eager to look for the opportunity.
One of the reasons I like to have nicer scales is because until you get to the decent blood summons you're going to be relying heavily on jaguar warriors (only non-capital troop worth recruiting), and they're pretty viscously counterable once people get a chance to respond strongly. I try to get some demonic backing before that happens. With that in mind, it's often worthwhile to see what sacrifices you need to make to get your pretender to be awake and researching from turn one, and dominion above 7 is often a good place to cut. All THAT being said, if you take one of the immobile pretenders like the blood fountain getting your dominion to 10 isn't nearly as expensive since you start at 4.