I don't think it would be 'too' busy. The dippers won't mind anyway, they'll be on the river
Its quite spread out between the abbey and the Strid so you'd be sure to find a quiet spot along it to watch from, if you didn't see one while you were walking.
The footbridge by the Cavendish Pavillion Cafe can be a good place to watch from, if it isn't busy.
When we visited, we saw more dippers upstream from the bridge but we also saw a couple downstream from it.
Again, good luck! Let us know how you get on!