Twoo - vewy twoo.
Well, I guess my advice might be this - yes, upgrade EVENTUALLY, but as 5.5 does what you need it to at this point, don't break your neck and go into debt to upgrade. Take your time and just do it when you have the resources.

When we talk about things WE can't live without - you've been living without them and doing just fine. It's $600 - most people don't have that lying around, so save a little here, a little there...

Good luck-
-Lew ;-)