I happen to like vintage-style skinny frets on vintage guitars - heck, I like them on most guitars...
FWIW during the '50s-60s manufacturers changed specs nearly as often as the auto makers of the day, as the fledgling post-war guitar market attempted to accommodate the needs of players adapting to rapidly-changing musical styles/tastes - it's not uncommon to find otherwise-identical instruments made mere months (even weeks) apart with
significant differences in fretwork, control knobs, pickup specs, available finishes, etc. (
viz. the '57-58 transition in Les Paul specs - P-90's to PAF's, gold-over-mahogany to darkback to cherry sunburst -
all within a 9-12 month period - followed in '59 by changes in neck profile along with the adoption of "medium-jumbo" frets, and two distinct versions of the '60 model as the "Slim-Taper" neck and "reflector" knobs associated with the '61 "SG Les Paul" were phased in shortly before discontinuation)...
That said, you might want to do a little research on the specific make/model in question, and find out when/if a change in fret specifications was adopted during that time period; while fat frets are unfortunately as much the flavor-of-the-week in certain circles as OM's with 1-3/4" prewar necks are over on the General Acoustic subforum they could well be original spec for your guitar, and as such I would also put it in the same class as a brand-new set of U.S. Royal 7.50-14 wide whitewalls for your show-quality '55 Chevy - an OEM-spec restoration that insures both continued practical utility and retention of value...
By the same token, if your guitar was fitted with narrow frets on that model/year I don't think it's unreasonable to expect that a knowledgeable/ethical dealer would in fact disclose such information prior to sale - again using my '55 Chevy as an example, collectors will pay a premium for a matching-numbers car as opposed to one that's been retrofitted with a 400 HP small-block crate motor and Turbo 400 transmission (regardless of what a total hoot the latter would be to drive
); although you may in fact feel differently (as you say, you like the way the guitar plays/feels/sounds) to me it raises questions of non-disclosure, and I wouldn't have a problem calling the dealer out on it if originality is important to you. BTW, I've heard tales of a very well-known/well-regarded dealer on one of the coasts (whose name I won't disclose here) who has earned a reputation for, um, "surprises" of this type every so often; although I've had no personal experience with the outfit in question I've hesitated to take the plunge on their otherwise impressive offerings - and you might want to look into this further before you take the next step...