As Alexander posted, if you capture or write down as much as you can throughout the week, there is less pressure when you brain dump.
What's interesting for me with a weekly (or more often) review/brain dump is how much of the "stuff" or ideas that come up are completely new ideas or are items that had been thought of earlier but weren't captured.
I'm managing to capture most of my stuff through the week, just by having something always at hand; be it a cheap memo pad or the voice recorder on my phone.
Then at the weekly review/brain dump, it's then easier to piece the separate thoughts and ideas together - which in turn trigger new ideas and projects.
It's "thinking of new stuff" versus "remembering what's been forgotten throughout the week"!
You said you're a songwriter, do you treat capturing song ideas etc differently to how you capture other general GTD stuff?
Interesting thread, best regards,