Is it practicality or passion that is driving your choices here? Do you have older Macs as well, such that a bridge machine between Old and New World would be useful? If so, I would suggest selling them both, and getting a fast Wallstreet PDQ with a floppy drive, max it out with RAM, and add a Firewire/USB Cardbus card, and a WiFi card. The new 12" Powerbook G4 sounds perfect for light couch surfing, and the Wallstreet can sit quietly in the background, connected up to all manner of drives and networks.

On the other hand, if it's a matter of passion - keep them both ... and get a Wallstreet as well

If it was a question of keeping just one, I would personally trade the Lombard in on a good Wallstreet, and keep the Pismo as the sine qua non of old-school Powerbooks.