The 12" Wacom tablet I had back in 2001 had a serial interface like com 1 was I think running Windows 2000 then. When I upgraded to XP I think I had to upgrade the tablet to an intuos 2 or 3 USB for Wacom was not supporting serial tablets could not find a driver for it. Still have the Intuos 12" but there no driver. The Intuos 2 or 3 bit the dust and was dumped into the recycle bin. I now have an Intuso 5 touch small and a intuos Pro small on my two PC. Both are USB and the Pro also does wireless has its own dongle Wacom is not using Bluetooth these days like they did with their older tablets. The Pressure sensitivity levels were also increased from 1024 levels to 2048. Perhaps if you have a young responsive body you can feel the differences between 1024 and 2048 mine can not.
if you have a brand new wacom tablet, why would you revert back to the one that's almost 15 years old? Stick with the new one. The old one was likely designed in the era of Windows 95/98/2000/xp... all outdated technology. There's zero reason for you to go backwards like that, especially if it was a gift for you?? Being 'worth it' likely doesn't apply in this siutation? Stay with your new tablet, it's fresher, newer and up-to-date. Plus, the older one is more succesptible to any sort of damage, and because it's old, it could break down at any time. Then what?
Regarding the funcionality, I really don't know - I used to use a Wacom Graphire 15 years ago, and I guess if I think about it, it would still work as well as my Intuos4, but it didn't have any extra buttons, the pen nibs were worn down, the tablet was all scratched - it was time to 'get with the times' and upgrade, so i did about 3 years ago.
One last thing - you can use both on our system if you want to. Just plug them both in, I've done it and it worked fine. You don't have to get rid of the old one, just use both tablets side-by-side and switch back and forth whenever you want to if it makes you more comfortable.