Yes, WMP7 and 8 were really bloated and slow. WMP9 is even more bloated, but it's not as slow as the previous ones, and you can just hide all the goofy features and windows you don't want to use. So I keep 6.4 on my system, but I use 9 as my main player. If you switch to the "compact" skin, it doesn't seem to consume any more resources than WMP6, and seems to start up just as fast.

To answer your questions, WMP 6.4 does allow streaming clips with multiple segments, and you can apparently open playlists (.m3u files.) It doesn't, to my knowledge, let you build a playlist and add/delete things from it. I also don't think it lets you open multiple files via drag-and-drop or browse.

I suggest at least taking a look at WMP9, disabling all the "send stuff to Microsoft" features, and switching to the compact skin. It's not as bad as 7 or 8. And I am definitely not a Microsoft sympathizer.