What's nice about the discount system in the cart (not saying that coupons wouldn't be good, they would be a whole lot better indeed!) is that you can use the built in text Grid (looks a lot like a spreadsheet) and you can highlight a full column (in your case discounts) and you can remove them all at once. Can't add them that easily unfortunately, but here's another tip:
Run sales on categories rather than just single items. You can set a sale on a complete category in one shot and turn it off all in one shot without having to do single item on/off and that saves a lot of time too. Where there's a will there's a way.
You can also set your home page settings to show Featured items and call that Sale Items. This helps with 2 things. People see your sales right up front, ... AND ... if you do decide to put items from multiple categories on sale, you will have that Featured items to use as your base to find all the sale items to turn it off (if you don't use the Grid of course).
Lots of little tips and tricks for things like this. Yes it would be GREAT to have coupons, but sales work too