The strange thing about monsters being fashionable is not that we choose to find all monsters fashionable at once but rather that we choose one monster to be fashionable at a time and generally caste the others by the wayside as uncool in the process. Pity the frankenstein's monsters. I've only read one series of late where they've had a mention. Luckily this series is a fantastic read and breathes new life into these creatures that are barely living in the first place (Simon R Green's Nightside series if you're interested).
So not long before vampires hit the big time, and I don't mean good old scary vampires but rather those horrible overly-romantic incarnations that don't have one ring of truth about them, were the werewolves. Now werewolves are often paired with vampires in a bid to keep both popular when both are fairly worn out re characterisation. Still, I do appreciate the return of the vicious werewolf to most of our current stories although I argue that they're heads and tails more capable of dominating the vampires if only someone would dare to write such a story (feel free to disagree but they do move about in the day, keep their reason and strength most of the time and aren't controlled by bloodlust all the time).
Even in children's stories, toys and movies there are fads and fashions. Fairies have had a fairly constant popularity amongst the young but the unicorns go in and out of favour with children. Gnomes, pixies and dwarves have fairly dropped off the radar except in the Grimm's fairytale remakes and the occasional Disney movie but there is a place for the scary but golden-hearted monster now. From Gruffalo to Monster's Inc the scary monster has been made over much like vampires have been (minus the romance), making them cute and cuddly if not on the outside then the inside.
Before the latest loves of vampires and werewolves (don't forget they had a few bouts of popularity and then stigmatism before) and scary golden-hearted monsters were giant beasts made so by radiation, furry but highly destructive gremlins and alien monsters (could be intelligent if they were lucky) who visited us or we encountered in our space adventures. While they all retain a certain place in our hearts because they were so loved they are in fact largely unfashionable now unless a master story-teller is at work. Newbies eat your heart out. Nerds and geeks both would complain that none of these were now uncool and they'd be right as far as I'm concerned but then I am one of the nerds and geeks. My vote is biased.
If you wrote on these unfashionable but still cool monsters now either of two things would happen. You'd either usher them back into massive popularity or you'd never see you work properly recognised, whether it goes to print or not. The trick to writing a popular piece is something most writers are unsure of and in fact are surprised by when it happens to their work some ten years after the initial publication. Why that is, is because fashion is a completely illogical thing.
Fashion is based on any combination of mass peer pressure, a sudden and unpredictable liking of the masses for something possibly considered horrendous at any other time that needs to be justified (enter peer pressure again), a sudden and unpredictable return of the masses to classic loves usually brought on by overdoing the previous fashion or by the reaching of middle age by the largest group of consumers (that old mid-life crisis thing comes into play), individuality being mass produced by a or many companies which are followed en masse by those desiring something 'new' or 'fresh', the popular opinion of a large group of people voting individually (the fashion most hope for as it is the most pure re fan appreciation), the announcement of something as fashionable by the elite of the industry which is then backed up by subordinates or anyone who wants to be in the know. It is quite hard to predict what is going to change when in any particular industry unless you happen to be in a position to change fashion. As a writer, there isn't much of a chance unless you're already doing rather well and get recognised by those in a parallel story-based industry.
That leaves writers with a simple choice. Follow fashion and risk being labelled a follower or a user of stereotypes. Or break fashion and strike out on your own, whether through subverting stereotypes and current fashion or by ignoring it altogether, to risk being unrecognised or quickly forgotten.
Personally, I'd say just write what you're comfortable with so that the world in your mind is portrayed in brilliant colour to someone else even though it is transferred through black scribbles. That way, fashionable or no, popular monster included or no, the story will be appreciated. You might find yourself stuck in the middle road of success for longer (or not if you're lucky) but you will have your work appreciated for its intensity.