The ECM 66B is a directional lav. Do you suppose that was a purposeful choice 16 years ago, or was it a choice based on noise in the studio, a small room or a very reflective environment?
If any or all of the above do apply, if you decide to get something new, be aware that most lavs are omnidirectional and that will change the sound.
Here's something else to think about. Omnis are supposed to be omni directional, but they are usually somewhat directional at high frequencies. In most of the news/interview shows I see, the mics are end address like your 66b or omni 77b and not side address like a Tram, Countryman EMW or Sanken COS11.
The 77b is more sensitive; -37 dB versus -52 dB, so if you have preamp noise you'd like to reduce, the 77b should help, but, again, it's an omni. The Audio Technica AT831R is directional and is more sensitive than the 66b. I have one and know it is wind sensitive too.
With the end address, you may get just a bit more edge on the voice. A side address lav doesn't give you that. The difference may not be much, but it may be helpful.
DIrectional lavs are usually prone to popping. Do you have any popping problems? Do you use a foam pop filter?
If popping is an issue try mounting the mic with the capsule facing down. Other options to eliminate P pops is to place the off center on a lapel if you're mounting it on a tie. For other choices look at the Sennheiser line of lavs their MKE 2 or 4 I believe is a cardioid lav.