Q: Is it worth it to upgrade a 2004 G5?

10.5 is the highest you can go with the OS.

Your local Mac store probably only have 10.6 in stock and don't have any more retail copies of OS X 10.5

Not sure which early 2004 G5 model you have, but you can install at least up to 4 Gbs of RAM.

You or the local Apple store would need to find and purchase an Apple Black retail DVD disc of

OS X 10.5 Leopard to install.

Amazon has it

http://www.amazon.com/Mac-OS-Leopard-10-5-10-51/dp/B0012RAVRC/ref=sr_1_5?ie=UTF8 &qid=1329851455&sr=8-5

From the above version I have listed,

You should be able to still get OS X 10.5 updates to download from to get you to the last release of OS X 10.5.8

Can buy this new or used.

Here's a much more recent version of 10.5.6 from Amazon , but new in box is really, REALLY expensive.

Buy either new or used

http://www.amazon.com/dp/B000FK88JK

from this version you'd only need to use one Apple updater download to get to 10.5.8

If you troll the Internet, youmaybe able to find cheaper than I.

I just gave you these links to show that it's more readily available, but you are going to pay much more than Apple's original $129 price tag for it.

Here's anpther site that may have it for just a little more than Apple's original retail price

http://store.fastmac.com/product_info.php?products_id=359

Here's a link that shows places that OS X 10,5 can still be obtained

http://lowendmac.com/deals/best-os-x-leopard-prices.html

Either you or the store are mistaken as to the computer model and its capabilities.  Some confuse the G5 with the similar-looking MacPro, but a store shouldn't. To get more information about your computer, go to the Apple in the upper left corner of any window, then "About This Mac", then "More Info..."  Copy and paste the information here, but omit the serial number.

I type this message from a PowerMac 7,2 2.0Ghz Dual Processor, with 8GB RAM 2 1TB WD Black HDDs and a flashed 6800 video card. There is only one thing I cannot do on this Mac that I cannot do on my varied Intel Mac's thats stream Netflix because it requires a newer generation MS Silverlight which no longer supports PowerPC. I watch Amazon streaming in HD, Hulu + in HD along with rentals from iTunes. Leopard got upgraded to the newest iTunes I have my iTunes match on this computer as well as syncing my iOS 5 iPhone. While PowerPC is "dead" to apple ot's not dead to many devs. I can even get webkit 2 browsers. Would I spend a ton of money on one nope is it still viable especially for the kids yes. My 6yo has my old G4 PB and thinks it's worlds greatest thing.