HI, You leave Warrnambool and head towards Penshurst through farmland, then spend a hour or so at Dunkeld, then take the road through to Hall's Gap through the Grampians National Park, a tourist attraction in ots own right. Stay a night or two at Halls Gap where you can see native wildlife, take walkd to waterfalls and scenic viewpoints.
Then head to the historic Goldfields towns of Ararat/Stawell and take in the Great Western and Pyrenees Wine Regions before getting into Ballarat along the Western Highway.
Nice one, UF. I second that as the most scenic route if you have a couple of spare days.
We usually travel direct, but we like to stop in Camperdown and visit Mt Leura for great views over the western plains. Another possibility is via Colac and Red Rock lookout. Those large lakes look fantastic on a map but are difficult to get a look at when driving. Sometimes they are dry. There is also a small town with elaborate carved tree stumps that we have been meaning to get out and have a close look at. I think it's Corindhap, but it might be Dereel. Some are visible on the main road whilst driving.
Ballarat - Sovereign Hill can take up 2 full days, there is so much to see there. The wildlife park is good. Lake Wendouree and the Botanic Gardens are a must imo. The Robert Clark Conservatory is free and always has a good display (last week it was cinerarias, primulas and cyclamen). There are some lovely marble statues throughout. The Ex-Prisoner of War Memorial is worth a look (as is the Arch of Victory 1-2 kms away). Have a wander through Fairyland - head to Pipers (large brick cafe/restaurant on the lakeshore) and turn left and walk along the lake edge for about a kilometre. With luck you might see a Rakali. You will definitely see Black Swans (you'll probably trip over them - literally!)
Another thing you might be interested in is the Ballarat Avenue of Honour, especially if you are coming in from the Grampians or Ararat along the Western Hwy. The turn-off is in Burrumbeet (route no. is C805). It's a 22 km long memorial to the fallen in WWI. A tree was planted for each local soldier who didn't return, and it's quite a sombering experience to see how many local lads didn't return from a conflict that was 3 months' travel away. This route brings you in under the Arch and very close to Lake Wendouree.