I've been looking at the daily sale plugin and realised that you can't actually apply any discounts to the products you've selected.
Is there a way to do this easily or could this be something to add in a future version of the plugin?
We don't have plans to add any discount features in the plugins since there are already a lot of options out of the box in nopCommmerce.
The Sale of the Day plugin allows you to pick up certain products but it is up to the store owner if these products will have a discount, special price or old/new prices.
Actually you can select any products and change the title to be "Product of the Day" rather than "Sales of the Day". The store owner has a lot of flexibility in the way to use the plugin.