Hang onto it for now. The big change for Macbooks and Macbook Pros will come next year when the Nehalem derivative comes out. This will be upwards of 25% faster than current processors, but more importantly will have better battery life on a smaller die. The change from your notebook to the new Macbook has better ergonomics, but from a power standpoint (cpu and gpu horespower, etc.) is only slightly better.
The good thing about Macs is the price is pretty well set. Meaning if your current Notebook is getting the job done, I would wait till next year or so for Nehalem, because the price of that notebook will be the same as the current notebooks, but you will get a nice boost of power. If your battery is slipping charge-wise, you can always get another battery and make due.
I will say having seen the new Macbooks they are quite slick, but I just think given the current power of your Notebook (it is still nicely spec'd a now 2 years or so after your purchase) it is worth the while to wait for the new architecture which is just around the corner. Really, with your notebook having dedicated graphics, you will be able to run Snow Leopard on your current machine no problem.
Still, I know how enticing new tech is. Coming from the world of PC's (I keep a dedicated pc desktop) it was and is always a temptation to get the latest graphics card or upgrade to the latest cpu, etc. That is what makes OSX so nice. It is such a nicely scalable architecture in the OS that I do not have to upgrade nearly as much to get pretty similar performance for a long period of time.
I hope this helps, and good luck either way you go with your decision.
