You have already watched a lot of older kdramas but I found some that are not on your Watch List.
Dal Ja's Spring- I have watched it recently and I really like it. It's about woman in her 30s and her friends and family. She is single and wants to get married but her life changes when she meet Kang Tae Bong- younger man in his 20s. It's cute noona romance and I liked support characters and their stories too.
Heartstrings- If you liked You're Beautiful you might be interested in this drama. Park Shin Hye and Yonghwa play lead roles. Plot takes place at college. FL studies Classical Korean music and ML is a singer and he has a band. This drama has great OST.
Personal Taste- FL is clumsy and naive woman who gets dumped. Her exboyfriend cheated on her with her best friend. She then meets ML of whom she thinks that he is a gay. There are lot of funny scenes because of this misunderstanding. The romance part is very cute and heartwarming. ML helps FL to be confident because he likes her as she is even with her shortcomings.
+ The Moon Embracing the Sun- it's 2012 drama but I think it counts as older/classic kdrama. It tells of a love story between a Joseon king and a female shaman against the backdrop of a Korean traditional palace and enemies vying for power.
Hope you enjoy!