Does detective Conan ever get taken seriously as an actual detective, instead of being seen as a mere kid by the main characters? Instead of hiding behind his subtle hints he gives and his voice changer to manipulate someone else as the case solver. If so, what episode does he get taken seriously?
He doesn't blow his cover, but regular characters pay attention to him down the line. This includes police inspectors. Though, you have to watch a couple of hundred episodes more. Around ep900 this becomes more prominent, but he's still formally just a kid and these kind of moments are more comic relief than anything else.
Of course, he exposes his identity to more and more characters, too, and those take him seriously.
There are multiple characters who pay attention to him for various reasons. Some know about his real identity and know his intellect, and others just because he's smarter than them.
- Akai Shuichi (Knows his identity)
- Rei Furuya/Bourbon (Doubts about his identity)
- Heiji Hattori (Knows his identity)
- Professor Agasa (Knows his identity)
- Yusaku Kudo and Yukiko Kudo (Knows his identity)
- Vermouth (Knows his identity)
- Masumi Sera/Mary Sera (Knows his identity)
- Detective Kids (He's a member of the group, only Ai knows his identity)
- Officer Sato, Takagi, Shiba, Shiratori (He's shown smarter than them)
- FBI - Rest of the Agents (He's shown smarter)
- Kaitou Kid (Treats him as a rival in terms of intelligence)
- Jirokuchi Suzuki (Thinks Conan is smart enough to rival Kid)
- Eisuke Hondou (Knows his identity)
There are several other characters who sometimes listen to him, like Kogoro Mouri, Ran Mouri, Sonoko Suzuki, Inspector Megure, and several other side characters.
Though the point that you're making, that he drops several hints and clues to find the criminal, used to be at the beginning of the series though. As the series progressed he takes on a somewhat direct approach to solving cases like asking others directly or sedating someone to solve it, as people started trusting him more compared to the beginning of the series.