I loved that scene too. I also thought Clarisse was a really endearing character. You can tell Miyazaki directed this movie with how it has a lot of touches that Ghibli later became known for.
If you do, I hope you like it!

Cagliostro is a bit more innocent than Lupin normally is, but I think a big part of the franchise's longevity is due to the variety it offers. You have everything from kid-friendly fare to more risque stuff aimed at an adult audience.
I thought his voice had a nostalgic quality too, but I could never quite place it. I think you're right!