A while ago I had the same concerns about having "just enough" collection buckets. Instead of looking at just the PDA vs. Paper dillema I mapped the pathways and processes that my stuff/information physically traveled, starting with the various inputs/inboxes I have (computer, notepads, Inboxes, & PDA).
Needless to say it was quite a web and it seemed rather byzantine. However, the exercise made me think about why was a particular path/process necessary. Then, I made changes and streamlined it to a point where each instrument/device/method had its utility defined. Anything else I just chucked.
Admittedly this was a huge tweak/hack but a useful one. I just reivewed the map I made a while ago and I can say that I've stuck to it pretty well since I first generated it.
So what do I use:
on the PDA: Life Balance (The master GTD program & To do list management) and Day Notez (Memo/Diary/Input) & the corresponding Desktop applications. I have DateBk5 but I dont use a lot of the functions such as the journaling
on my person/paper:a Clairefontaine notebook for meetings and a Hipster PDA for all other times.
As I said the mapping exercise was very useful in tying all the gadgets and programs I had and made me justify their usefulness.
Hope this helps...