Agree with the above. The itinerary is totally doable, giving you enough time to see a variety of sights as well as soak up some of the more tranquil places such as Sucre and Salta.
I lived in Sucre, Bolivia for 5 months, it's such a beautiful city with loads to see and do, especially if you know where to look! Don't miss out on the dinosaur park and Maragua trek.
Potosi can be done in a day trip on route to Uyuni. Catch a bus early in the morning, or if you've got a group of people, a taxi (super cheap), and make your way to Potosi for about 10am. Leave your bags in the lockers at the bus station, go walk around the city, do a tour of the mine and the National Mint, grab some lunch, then catch the evening bus to Uyuni around 6 or 7pm. You will arrive in Uyuni around midnight. Just make sure you pre-book your hostel and salt flat tour (highly recommend Red Planet), so you can head off after a good nights sleep!
Getting to Sucre from La Paz, I recommend taking an overnight bus with El Dorado; was quite a pleasant experience really.
For more info on buses, transport, hostels and heaps of fun things to see and do in Sucre and La Paz, feel free to check out my websites: Sucrelife.com and Lapazlife.com
Re other places, personally I fell in love with Mendoza. We stayed for a week at Lao hostel which was absolutely fabulous. Highlights were a day at the hot-springs in the mountains, a long lunch and wine-tasting at Bodega Nieto Senetiner, and dinner at the closed door restaurant Ituzaingo.
Also since you've already been to Mendoza, if you have time and love wine, would definitely try and head to Cafayate for a day or two. Great little place with lovely bodegas and restaurants.
Hope that helps a wee bit :)