As long as Yamato & Bandai keep pumping out new toys, updated versions with better & newer gimmicks, paint jobs, articulation, etc. It will be harder for the older versions to rise in value. I'm sure there are those out would disagree, but now a days it more or less New flavor of the month vs. I gotta have that rare V.1 1/60 to fill the gap or that older 1/55 Takatoku model VF-1A CF.
Lets be honest 10 years ago, if you had a 1/55 VF-1S Hikaru DYRL Strike, it might have been worth close to $1500.00 or more. ( I Still have mine, box and all & will not sell it, to much personal value to me) But know a days your lucky if you can get $250.00 for it, There just to much to choose from now a days.
I think if toy making were to halt for say 3 or 4 years, prices on the old 1/55, V.1 & V.2 1/60's would go up in value. And the now depreciated 1/48 would become what it already is in my eyes which is a collectors item. Especially since its scale size 1/60 from here on out.
The bottom line is this, If you bought the toy, you like it, hell you even love it and could never see replacing it, then thats all the value you need. If its a matter of resale, well thats up to the buyer & economy.
My 1/3000 SDF-1. VF-1S DYRL Strike 1/55 circa 1984, 1/8 Mospeada Ride Armor. Never selling them, now way, no how.