Yes, keep it. As I said, the monitor won't be locked to the G3, so if it bites the dust you can get something else and use the monitor with it. (Just a shame it's not an early G4, though - those are much nicer than a G3, but at least it's a pretty decent G3.)
If you do sell it, though, grab an eMac if you want a desktop machine. As others have mentioned, they're not bad machines at all, especially the last revision.