As most trails involve more hills, I think you will get a lot more strength. Technical downhills are good for practicing staying light on your feet and working on turnover. I try to get most of my runs on the trails, and I feel much stronger overall because of it. Less beat up, too.
I do like to do one tempo run on the roads (or a flatter section of dirt). And occasionally I'll throw in strides (also on roads or flat dirt).
But if trails are easy to get to for you, I don't think there is any reason to not do a buildup like this. You might also have fun throwing in a late fall/early winter trail race if there are some around.