The only reasonable one is a gravel track which climbs 200ft in just under 0.4 miles and Strava lists it as being an average of 6% gradient.
Is it worthwhile doing hill rep's on something like this or would it be too small to be of any benefit?
Sounds like plenty of hill to train on, especially if it's representative of climbs on your local courses as BermudaBrown notes below. Or, if you are planning to race somewhere out of your area that has longer climbs - by time elapsed - a "fudge" you can employ is to tack a few minutes of intensity on the flats to the bottom before you start the climb and/or the top after you crest the climb. e.g. if the actual climb takes you 5 minutes at an intensity you can maintain for a few reps, but you want to become accustomed to a climb of 10 minutes duration, just add a total of 5 minutes at similar intensity on the flats before/after.
That being said, if your goal is to become strong at longer climbs of say 30 minutes, the whole concept of intervals is to go at a higher intensity for shorter periods of time, than you could sustain for your actual event. In other words, doing multiple reps of a 5 minute climb, with a brief rest in between each, at a higher intensity than you could maintain for a one shot 30 minute climb, is actually great training to cause adaptations that will help you for the 30 minute climb.
Rules of specicifity apply - i.e. you will become strong at hills like the one you're practicing on.
I'd go for the hill reps on it - chances are your nearest race tracks also only have hills of that size.