Most def change the fluid, plus it will make life alot easier when your installing an empty dif rather than one filled with gear oil...

I did the same thing on my 08 Base and i loved the change. Sure its crappy VLSD but it really did change how the car drove, and if you can get one for cheap (like i did) why not upgrade?

Good luck with the instal, it is fairly straight forwards. I re used my stock bushings btw, i was at around 30 or 40k miles like you so i figured they should be fine for another 20k or so, ill change them when i get to that point or when they start wearing.