Dealing with a too low word count while avoiding "fluff"

I have done it again. Seven weeks ago, I finished a first draft of a novel, coming out at a paltry 50,000 words. Perfect for NaNoWiMo, but not very useful anywhere else, where most publishers require word-counts of 70-100K.

Still, when the draft was finshed, I put it away to "marinate" for a few weeks thinking that when I picked it up again I would find enough plot holes to fill and add to the word count. Alas, it did not work that way. The story flowed fine as it was and all I could find were things to cut, such as cliches and adverbs.

What does one do to add to a second draft? Most editing advice is all about cutting. When do you add to a story? Where and how much? I don't want to put down a few thousand words of extrapolations on the blue of the sky, the green of the trees, and the fine architecture of the buildings in my setting. Some authors can get away with this, but I am not Anne Rice. I feel this would slow down the plot. I don't want to do an accessory by accessory run-down of everyone's wardrobe, I am not Laurell K. Hamilton.

My novel is to be a Regency Paranormal Romance. It was a blast to write. For inspiration I reread a few of my favorite Regencies and after a few hours of agony thinking I could never match such greatness, (Do any of you do that too?) I noticed a few patterns that enriched the stories and contributed to word count. Here are a few ideas.

1.) What are the current events happening in the story? Can you tie it in to the setting/ plot? Example: My story takes place in England in 1821. King George IV was crowned in July of that year. Perhaps the characters could have a scene during the coronation!

2.) Are you involving all five senses in your descriptions? I seem to neglect taste and smell a lot. Perhaps my character can complain about the stink of the Thames, since solid waste was dumped in it back then.

3.) Is there a transitional paragraph in the book that could be livened up into a dialogue scene? I had a paragraph in which I described my heroine's scandalous behavior which resulted in her being shunned by some crowds. Perhaps I can replace it with a funny scene in which society matrons are gossiping about her.

4.) Remember to "Show" and not "Tell." I know, I know. That declaration is made in every work regarding the craft. Because it's damn good advice. I repeat hear for the simple fact that "Showing" usually takes more words. i.e. "She was angry" vs. "She threw the vase, missing his head by inches." (I know, that's a cliche and I didn't use it, fun as it is.)

That's what I have so far, and I'm now eager to get back to work. I welcome any new tips you all may have.