Yep, have they ever.
Bought the red one for $6,500NZD in 2009, it's now worth more than $25,000. High km's though, nearly 300,000 i think.
And bought the four door for $3,000NZD (from Dad, he was wanting $6k) in 2005, it's now worth more than $30,000. Despite being almost in factory condition (except for exhaust tip and some polished parts in the engine bay).
Back in the 2000's/2010's we (my family) were buying R32's for as low as $900... Bought another for $1,200, another for $1,400 or so. Wife's Dad got a couple for under $4,000 i think, wifey's one was bought for $2,000 or so in 2007 and is now also worth more than $25,000.
Great the cars are increasing in value except for the fact the annual insurance premium goes up with the valuations. I'm paying over $700 or so a year for each car. Up from less than $400 only a few years ago. Still got full insurance despite them being stored away. Too much fine print with insurance companies these days, so don't want to give them an easy way out of paying if something happens.