Values?

Don't waste your money upgrading old hardware. The G4's have significant bottlenecks that make fast CPU upgrades a poor value.

Cube
CPU- $150 for cheap 1ghz single to $450 for high end dual 1.5ghz.
HD- 120gb hd (biggest it can support) $45
Video- $75-200
Memory- 1.5GB $25
Total- $300-$720

G4
CPU- Dual 1.8GHz $425
HD- 1TB $100
Video- $75-300
Memory- 2GB $45
Total- $645-$870

To upgrade either of those "extensively" would end up costing more than a Mini for FAR slower performance. The Mac Mini will be significantly updated in January, save your money for that and mod it to fit inside the cube or G4 case. $700 will also buy you a dual core G5 that, while it won't be as fast as a new mini, would still walk all over those upgraded G4's in every category.

I spent $60 on my G4 to upgrade the CPU, video, memory and add USB2.0. Its no speed daemon but it makes a great backup/diagnostic/emergency computer with less than $200 into it.

 

cubes look scary to work on:
http://www.wap.org/journal/powermaccube/powermaccube.html
(and shouldn't they be "iCubes"? iSteve must have suffered an iSenior moment.)
here are some overpriced g4 cubes:
http://losangeles.craigslist.org/sgv/sys/971749015.html
http://losangeles.craigslist.org/lac/sys/970665086.html
http://miami.craigslist.org/brw/sys/971266473.html
http://minneapolis.craigslist.org/sys/970218403.html

how much ram? install cd? unless short on those, you could rob the cube for (some) powermac parts, though you could use the cube til it dies.

(where's the filter, aeration?)

how much ram in the hdd? install cd?
(btw, doesn't macrumors send "price this" threads to the misfits?)

 

Bettas don't need a filter or pump.

 

I'd say the Cube is worth about $150 and the MDD is worth paying about $360 for. Of coarse, RAM is a determining factor as well. Older RAM for those systems is starting to become expensive again, so if they're already maxed out/have a usable amount installed that always helps the price some.