"Your book needs to be longer" They didn't even read it. Not that I blame them, it's business... but is that really a criteria? Has anyone ever put a book back on the shelf at Borders because it was too short?
Abraham Lincoln said "A man's legs should be just long enough to reach the ground." Same thing applies here. Tell the story, when it's done--it's done. Why should I go back and describe in detail things that the reader's imagination will likely fill in? Some writers do that, they go on for volumes describing a non-existent town that looks like any other town. Why not let the reader will make up the location?
If you're building an alien planet, fine. But to describe the look of a ma-and-pa shop in hometown USA is kinda silly. Describe the important things you want folks to look at and they'll stand out.
A story should be long enough to say what it needs to say. Then get out before people get bored.
Maybe I'll never write a novel. Just doesn't seem to take me that long to get to the point.