The original sentence:
"Our bathrooms are filled with gels, waxes, hairsprays and sea salt sprays that have never been used more than once."
And the reduced version:
"Our bathrooms are filled with gels, waxes, hairsprays and sea salt sprays never used more than once."
I don't know if it sounds clumsy reducing the original one.
The reduced example is grammatically incorrect. I don't believe this statement can be reduced (at least not in a way that doesn't sound funny to my ear).
Please note that the first example is a bit inacurrate because the rooms are not filled with those items. "Filled" means so many of those items are in the room you can't open the door. Here are some better examples:
Our bathrooms include gels, ...
Our bathrooms are stocked with gels, ...
Our bathrooms have gels, ... (this example may not be preferable due to the repetitive use of "have," but that's a personal choice).
Another way to express the idea is to focus on the items, not the bathroom itself:
The gels, waxes, hairsprays, and sea salt sprays found in our bathrooms have never been used more than once.
Finally, you might consider using "not" rather than "never."
The gels, waxes, hairsprays, and sea salt sprays found in our bathrooms have not been used more than once.
You can use either one, but "never" is a word that, in this context, suggests emphasis. It could be interpreted as enthusiastic, but it could also be interpreted as defensive ("We never do that!"). Using "not" eliminates this issue by removing the emphasis. It's a simple statement of fact ("We don't do that").
Which is better depends on the nature of your business and the culture of your guests. If your guests react better to using "never," use it. If they might react negatively, don't use it. Only you can decide which to use.
