Actually, Taft offered their stake in all parks to Paramount as part of the sale. Paramount cherrypicked and elected not to take on Australia's Wonderland because of the distance and difficulty in managing the park remotely. It was nothing to do with whether they had a minority stake or otherwise - they could still have sold that stake.
I'm impressed! Yes, you're pretty much right. I'm not 100% on whether Demon was a Taft project or a paramount one - although i'm leaning towards it being Taft due to the lead time.
As for investment into the park, and the second-hand nature of many of the parks attractions, I think we'd have seen Paramount \ Cedar rotate some rides around (Six Flags style) and we'd have seen some newer attractions move around a bit. I think if Paramount had been willing to take the park on, it would still be standing today, most likely under the cedar fair brand..