I can actually think of a couple. First - I recall credit being given to Steve Austin for his observations on how trees were observed to sink in Spirit Lake below Mount St. Helens. The second is Lord Kelvin’s idea that thermodynamics could be used to establish the age of the earth. His technique was well thought out, but his answer ultimately turned out to be in error. (But that was because the data available to him was lacking some factors that were not understood in his day.) And of course, Lord Kelvin’s work on the age of the earth made him an old-earth creationist.
Thank you for playing, and for drawing the floating trees to my attention. That is indeed an attractive observation. But I think it would be wrong to give Mr. Austin any credit for either the observation, or any associated idea. I can't find any reference saying that he discovered the trees in Lake Spirit, and his 'idea' seems to be that because some trees can be transported by water and deposited 'upright', that therefore this is evidence for a global flood (correct me if you think I have missed his point). That idea cannot possibly deserve respect, especially coming from someone who cites his own PhD but clearly ignores screeds of the evidence that exists within his field of 'expertise'.
I think if you are going to give Kelvin as an example then we could open the door to anything proposed by Newton and many others. But those are examples of respectable scientific ideas explained by people who were creationist. The thermodynamic age of the earth isn't really a creationist idea. Kelvin may well have made a creationist interpretation of it, but that creationist interpretation doesn't deserve any respect because it's not founded in evidence.
And, as you quite correctly point out, the idea is wrong and has been modified to include radioactive sources of heat within the earth. I think Kelvin would have quite happily ignored radioactivity unless it had been pointed out to him by Rutherford and others, and even then he stuck fast to fixed ideas that fitted his views of how long it was possible for life to have inhabited the planet. Although he made major contributions in electricity and thermodynamics he was in denial about a lot of technology that was about to be invented, most famously radio and X-rays.
Stuart