When I said admiration, I meant admiration in the aspect of compatibility. (Shinichi admires this and that, so he sees her as a viable option as his girlfriend)
And yes, if a girl has a sexy body, she would be of interest for Shinichi. Ran DOES have that body. (As for Shiho, it is unknown yet)
Yes, Ran does know him well since they are childhood friends. But during the case, it was much deeper than that. She started weeping out of nowhere (because she could sense that Shinichi was nearby) It's like they have a "psychic" connection between them that requires more than being childhood friends.
Mutual interests is different. When I say "opposite", I am referring to personality. Two people can have have mutual interests, but can be totally incompatible because of their individual persona. But on the subject of mutualism, (it's kinda like what you said between Shinichi and Ran and how their childhood is the only thing mutualistic between the two) Shiho and Shinichi are only mutualistic when it comes to their situation with the BO and the fact that both of them have shrunk. And both of them are intelligent in two different aspects: Shinichi with deduction/mystery/random facts and Shiho with science. So their level of knowledge doesn't mean they are mutualistic in any way.
The best relationships are made between "closest friends", not just any friend. One friend must stand out more than the other (Ran *cough cough*).
And the main reason why Shinichi doesn't tell Ran is not because he doesn't trust her, it's because he knows Ran will do anything to save Shinichi's life, even if it means sacrificing her own. Also, he doesn't want Ran to constantly worry about him and his condition. He's already hurt her enough. (he wants to defeat the BO solely because he wants to return to Ran, which he has stated multiple times before).
And lastly, I have to 100% agree with Saki's old post:
I think both sides (ShinRan and ShinShi) have equally good arguments on compatibility but IMHO, I think a person should be with who he loves best regardless of who would be a better match for him. So, my vote goes to Ran here because Shinichi loves her* and she loves him in return.