Naaa, most of the value is ‘lost’ as soon as it’s not new, the klein might have soem retro value, can’t imagine the Cake has much, the road bike might if its steel.
Either:
Run into the ground from new/sh depending on budget/preference
Buy s/h and swap every so often (the Hora method)
Buy new and accpet its an expensive passtime (the Ton method)
You could probably argue that a 3 year old bike thats been looked after is worth half its new price if the models still available. So maybe sell it then and buy another new one then your only loosing about the same assuming the value is negligable after 6 years.
I seem to do the opposite, buy s/h but good condition and run it into the ground, seems the cheepest way.