monogram necklaces

I have been seeing these everywhere lately and decided that I want my own. I am also thinking this may be a good way to spend my graduation money because it is something I will have forever. Here are a few I like:

Necklaces by Sarah Chloe were featured in this month's Elle Magazine and I loved them. 

I also have been wanting to get a signet ring for quite some time and Sarah Chloe designs them as well:

These are SO popular right now that I wonder if it is just a passing trend. But on the other hand, its not like your initials will ever go out of style. Is it worth spending a lot of money on a monogram necklace or signet ring with the goal of having it forever? Or better to purchase a less expensive one and enjoy the trend while it is hot? Will this turn into the "Carrie Necklace" type of situation where everyone will buy a little gold necklace with their name on it and then all of a sudden the popularity will disappear? hmmm