You said that you can be completely opposite from somebody and love them.
And while friendship is a step in a romance you do need things that are in common. I don't think Ran really understands Shinichi at all and vise verse. A lot of the confusion wouldn't exist. What makes a relationship are similarities, sexual appeal, and of course the feelings. If you don't have anything in common then that brings down compatibility. That it not a fact you can get around in love. They don't have a single thing in common except for maybe morals- but you need more than that.
Gosho could very easily surprise us with a different ending. Ran may die. Shinichi may die. He may stay as Conan. I'm personally betting on Shinichi and Conan separating but that's just me. He could even say "they started dating but departed to go different ways after high school".
Haibara respects him, yes. But I doubt she holds any romantic feelings for him. Relationships have everything to do with similarities. A couple of things may be different, but you need similarities for things to talk about, how to raise a child, how to pay the bills, RELIGION, what friends to make, what the house will look like, jobs- all of that. If you just understand somebody that doesn't mean you can raise a kid with them. You probably wouldn't be able to settle on a religion (if you want one), you may not agree on how much to spend each month, and what in the world do you expect for them to talk about with only understanding each other? Shinichi would always want to talk about Holmes and she'd want to talk about the house, her experiments, her job- the normal things a wife talks about (lol. XD). Shinichi needs a woman who won't chatter on about that all day, don't you think? XD
Just because you understand somebody doesn't mean you can be in a relationship with them. It'll get you to a "friend" point but no further. She only understands that area. Every other part of him remains a mystery to him. She can't understand more than half of the things she does! XD And so what if he saved her life numerous times? He's saved Ayumi's life, and Mitsuhiko's, and Genta's lives several times as well. It's what he does. My point is that similarities play a large role and with similarities, understanding comes along as well in time.
And in't believe that little line at the end there until Conan says it straight to her face. Until Gosho writes it and THEN I will agree that he thinks of her as a classmate and nothing more- because to me there are a lot of signs saying that that may not be what Conan thinks.