Is writing easier the second time around, or just when you have a 'fresh' idea?

As I've said before, I'm having trouble editing my work because the idea for something new keeps nagging at me. I've written pages of something new when I'm supposed to be focused on something I've already written. Maybe it's because writing gets easier the more you practice, or maybe it's because the fun part of writing is writing something fresh. When you're editing you're not really adding anything fresh. You're looking at what you've already written and trying to find the errors/see what can be built upon and added to. Maybe my issue is time. Maybe I need to sit down and write for a little while and then focus the rest of my time on editing. I've thought about having a writing day and having an editing day. Something like that could be interesting for me.