I'll vote for upgrading-- you will be pretty happy with the new Sonar as a lot has really moved ahead since x3e.
The included VST's, plug ins and for me the new editing in PVR is worth the ticket price.. There was lots of discounted offers for upgrades recently.
I think the trouble with the demo is you don't get a lot of the built in VST's and plug ins.
You can always buy it for just one month?