For future reference:

1gig PC-2700 stick for 12" G4 Powerbook : $89 from Ramjet. $44.95 from OWC.
Would move Knave from 640 to 1184. (128 meg soldered to mainboard)

2x2gig PC5300 DDR2 667MHz matched DIMMs : $85.99 from OWC.
Would move Athena from 1g to 4g. Ramjet sells a 2x1g kit for about the same price and as of this timesink does not list a 4g kit.

Putty Knife : ~$6.
Required for any form of surgery on Athena. Which looks to be a major pain in the ass any way you cut it.

Superdrive for Athena : ~$100 from OWC.
If I'm doing Major Surgery, I may as well go all the way. Though Maniac and Minerva both have 16x superdrives in full-sized ATA bays. And those drives, should one go belly up, can be replaced for $20-40 and a bit of sweat. Oppose the Total Butthurt of working on Athena.

Searching for 2.5" HDDs reveals that a 3.5" in an outboard is going to offer MOAR GIGS for the same price, where "price" includes hassle, butthurt, surgery, backups, data transfer, etc.

OWC Mercury Elite-AL Pro USB2/FW400 500g drive : $135.99 from OWC.
Empty ("0g") SATA enclosures retail for about $70, so getting the thing with a 500g drive is a good balance of price/convenience. More options here. 320g 7200rpm 2.5" drives start at about $150. No contest.

Looks like an OWC order or two is in my near future - probably one for RAM (soon) and another (later) for the disk.

Which reminds me, I still need to file COA with my bank.