We've moved into (in my opinion) a more philosophical question with art and photography.

To answer this, you need to figure out what is your definition of "good photographic vision?"

How do you measure the artistic value of a photograph? To me, that is a very subjective question; much like judging any type of art is.

I have had the luxury of visiting many of the worlds finest art museums, and not every work of art that is on display had artistic meaning to me. In fact, I now know that I prefer modern art to the the classics.

So to get to your question: Spin it another way: Why do you think your photographs lack in artistic value? Are you judging your own work yourself? We're all probably our own harshest critics.

My definition of art is: any work that evokes an emotional connection. What is your definition?

How does one get better?

Like all artists, you need a mentor. Study the works of photographers whose work you admire. Every great artist spent years studying the works of other great artists.

Like many artists, you may need to leave your home. How many great authors, painters, sculptors, have traveled to find inspiration. Perhaps you need your own "walk about" (yeah I'm a Lost fan :)

Take risks. Since you enjoy nature photography, how about trying a different type of photography, to get you to think outside the parameters of nature. Street Candids, or still-life, macro, sports. A subject you don't have the "technical" mastery of will force your right brain to engage more.

Experiment. If you always shoot nature with tele's, try grabbing a wide-angle and see what you get.

Practice. The idea that creative types just know how to be creative is false. Artists spend so much time honing their skills, and it's the same with photography. The Beatles played shows day in and day out for years to hone their musical skills. Malcolm Gladwell famously wrote about 10,000 hours in Outliers. You said you're "new" to photography, so give it time. If you shot photographs for every hour of every day for the first year you owned your dSLR, you'd still need over 1000 more hours of practice :)

Be a true Renaissance man (or woman). Try other creative outlets. Ansel Adams taught himself piano. Lessons learned in one art form can directly influence the works of others.

Submit your work for critique. Enter photo contests, find a way to get into an art-show, submit your photos online to places that give honest constructive feedback.