There are indeed. One of the best I saw was inside a dummy radiator. Same design as the rest of the house, but with a secret opening. Although that wouldn't be a suitable solution for coins.
Another was a specially upholstered sofa, again with a secret entrance to a hollowed out section.
Most thieves are opportunists and they're not going to be long inside any property. They'll go for the obvious. It wouldn't include such things as an opening in the floor midway underneath a living room carpet.
The loft idea was only ever meant as a very short term means of storage if you were going to be away from the house for a couple of nights. Not really time to do any damage. especially if well protected.
It's definitely a factor for strong consideration with regard to your collection. After all, you wouldn't leave £50k in notes in a briefcase on the sideboard.