The change of candle heights, the addition of cobwebs, and maybe some color would help. But would this be a regular feature/get normal use in your home off season?
If so, you could still do the cobwebs, maybe make some alternate candles (PVC and a hot glue gun can do wonders), and maybe give it a sponge bath with some tinted dishwashing liquid. That way you could give it a bath and change it back as needed/wanted. Adding flickering bulbs would help too. You can put spiders in with the cobwebs, and depending upon the scene you use it in, your cobwebs could run down to a table, and or have some captured creatures caught in the webs.
You may find that having only one or two of the candles "lit" would help in the "creepy factor", so much depends upon how and where you would use this in your haunt.