My Dob does seem to benefit in terms of Go To accuracy by having the base board level. I say seem, as even when levelled it can be hopelessly unreliable some times, and work well at others. I have not figured out why. I think the bearings and motors are not really up to the job - this is the SW 12".
But since I started making sure it was as level as I could make it, it has at least improved. I use a circular bubble level.
The thing is I don't know why that should be. In my head, if you have done a 2 star, or certainly with a three star, alignment I always think that should be enough information combined with an accurate location and time for the computer to work everything out that it needs, level or not. But level it seems to need, anyway.
Not sure of that helps.