I can't recall the floating hand (and it's the sort of thing that would stay with you) but the bit I found most terrifying was an anecdote about a pitch black night and a heavy goods lorry rumbling up Nantycaws Hill (I didn't look this up - the name has stuck for over 30 years!).
There were two guys in the truck and as it ground its way up the lonely, dark hill, the headlights picked up something on the verge ahead. Because they were going slowly the men had quite a few long seconds to see what was there. Two aliens, one tall and silver, one squat with an enormously wide head, were standing in the darkness. They were both holding a single unidentifiable object between them. The didn't move as the lorry churned past, a matter of feet from them. This was in the middle of nowhere, and as the lorry passed, the silent figures were swallowed up by the darkness again.
I. Did. Not. Sleep.
Like your recollection, Oldrover, the thing that was so great about about the Dyfed business was the odd details. The scrunching paper sound you mention, and for me the ridiculously wide head of one of the aliens.
Oh I remember another bit. A teenaged girl was woken by a light shining in her bedroom window. She pulled back the curtain to find something looking like Mr Punch staring in at her.