Change light fixture and paint vanity. Choose your favorite shower curtain and some accent that goes with it. When you tire of that, it will just take a shower curtain change to refresh. I do like the one you have though!!

If you are going to leave the cabinets that color, I would change the knobs to a darker color to bring out the color of the countertop. I would also frame the mirror to add depth. I did mine a year ago and it was so easy, I purchased them from http://www.mirrormate.com there are many choices in style, color, etc. Easy to measure and hang. I did mine in less than one hour. I would also consider adding more color either in the curtain, bath mat and towels or painting a wall. Enjoy your decorating time!

Start by picking a color you like. Paint the vanity. If you want a simple look, paint the walls a shade of the same color. Definitely replace the light by going to a lighting store. You will need to give them the size of your mirror and perhaps the size of the room. If you want to change the size of the mirror it would really update the look of the room.

People are using smaller mirrors, sometimes with an ornate frame. It could be round, oval or square. If you don't want to change the size of the mirror, you could still add a frame for it. Definitely change the hardware on the vanity. It will need to coordinate with the new light and the frame around the mirror if you add it. It should also coordinate with your sink and bath fixtures.

If you are thinking of making changes to the fixtures, polished nickel or antique bronze are in style now. Your towels and shower curtain will be the crowning glory. Make sure you choose them wisely. Spend more money than you usually do and pick a color(s) that coordinate with the walls and each other. Would love to see pictures when you are done.

I would update the light fixture, cabinet hardware, faucet, and paint the walls a shade between the cabinet and counter (marginally lighter than the counter). New finishes should match. Add some color via shower curtain, towels, etc.

Cabinet hardware is always a good update. I've always liked the look of our monarch collection in a bathroom: http://www.houzz.com/projects/270903/Monarch-Collection

As mentioned above, you could add a narrow frame around mirror or to give room a bit of color, small glass tiles below mirror (see second picture), that coordiante with your shower curtain. Updating the vanity's hardware and faucet will make a big difference also. I would paint the vanity the same color as the walls. On the wall opposite to the sink, add a towel holder that compliments the hardware and a framed poster. [houzz=]; [houzz=]; [houzz=]; [houzz=]; [houzz=]

Hi...Aside from painting the vanity and changing the light fixture...you have a great looking bathroom. Love the size for starters. Also very much like the curtain, but would purchase another one to give it more fullness versus the stretched out look it has now.
The ideas and pic that Maureen above has featured for you I think are great choices. Especially the Stained Glass Mosaic Tile, which I can see on the entire back wall of vanity and toilet area.
As for the mirror, I like it and would keep it. I just don't want to clean it ;) So big I mean. Framing it is a personal choice, but I tend to like it the way it is as it continues the contemporary look of the room.
The vanity base would look great painted black matte finish with brushed silver hardware. I did my kitchen base cabinets that way and love the look. Pic attached for reference for you.
Black and white is classic...So if you like it, as I do, I'd suggest going with it and making it bold.
Again, you are quite fortunate to have such a large room to enjoy.
Have fun with it...take your time also so you do not regret quick purchases later. I'm sure you will do a great job.
PS: I was going to add my kitchen cabinet pic, but can't seem to get it uploaded here for some reason. Will try to add it still. Sorry.