Somehow - I seemed to've missed the part about giving up a collecting interest to concentrate on another - though I do know that it happens.
I've collected, dealt, appraised and written about Post-Civil War American Mlitaria for a several decades, now - specializing in WWI SSI's and Collar Disks, along with Theater-Made insignia, and AAC/AAF, Airborne, Cavalry and Infantry material.
I started as a Great War collector in the early '60's, and something like that opens a lot of 'windows' (and trunks and closets and drawers) when you're actively looking, since a helluva lot of vets were alive and kicking - as were a couple of Spanish-American War guys.
To a young historian - it was a literal gold mine - both of militaria and of history, and those guys 'wanted' to relate their stories to an interested ear.
The thing is - a 'collector' collects...
It makes little difference 'what' he collects - as long as he's doing it.
He may be far, far removed from what his normal interests are - so he'll find other things that strike his fancies until he returns to his 'hunting grounds'.
Were he to be stranded on a deserted island - once he figured out warmth, shelter and food - he'd probably beach-comb for shells, or something of like matter - just to satisfy the need.
For example - I lived in Illinois for awhile - and they had some of 'the' best gun shows you'd ever want to attend.
'Then' - gun control legislation dropped across that world like a stone, and everything that shot was requiring paper and permits.
As a result - I started added the collecting of US-Issue Combat Knives, along with Gun Tools/Accouterments, since no one else did, and brand-new examples were leaking out of Rock Island Arsenal on a daily basis.
Good times, those.
There are a lot of 'niche' items that both flesh out an Impression, and if you know the field - they 'can' be had reasonably - unlike almost 'anything' from Deutschland.
The cachet of 'amazing value' to that materiel has risen steadily since the '60's, and there are far too many really well-done fakes extant to ever be of interest to me, so what Axis stuff that I do get is included with the American militaria I pursue, and is sold/traded quickly - often times paying for what I laid out.
Good Hunting.
Vaya,
Scouts Out!