The comparison between a Cessna 172 with a 180-horsepower conversion and a stock Cessna 182 Skylane touches on a perennial debate in the piston GA world, one that resurfaces regularly on owner forums and at aircraft-shopping decision points. The core tradeoffs are well understood by experienced owners: the 182 offers a heavier gross weight airframe, a constant-speed propeller as standard equipment, and the Continental O-470 six-cylinder engine producing 230 horsepower, while a 172 with an aftermarket 180-hp conversion (commonly using a Lycoming O-360 four-cylinder) gets much of the useful-load and climb-performance benefit at a lower acquisition and operating cost. The original poster's observations are largely accurate—cruise speed differential between the two is modest, often only 5-10 knots in real-world conditions, and useful load numbers can be surprisingly close once the 182's added structural weight and fuel capacity are factored against a converted 172's more modest but still respectable payload. The fuel burn delta favors the smaller-displacement Lycoming, which is simpler, lighter, and generally cheaper to overhaul than the Continental O-470, a point that resonates with any owner tracking direct operating costs on a per-hour basis.
For working pilots and operators, this kind of piston single comparison may seem tangential to airline or business jet careers, but it matters more than it appears. A large percentage of professional pilots—especially those flying Part 135 charter, aerial survey, flight instruction, or corporate light aircraft—cut their teeth on exactly these airframes, and many maintain currency, build hours, or fly personal aircraft in this same 172/182 category. Fleet operators making acquisition decisions for training organizations, banner-tow operations, or utility/backcountry flying face precisely this same math: acquisition cost, parts availability, engine overhaul reserves, and useful load all factor into total cost of ownership calculations that scale up conceptually to turbine fleet decisions, just with different variables. The 182's broader used-market availability, as the OP notes, is a real factor—liquidity and parts commonality reduce downtime risk, a consideration that echoes larger fleet decisions where operators favor common types (King Air, Caravan, etc.) precisely because parts, maintenance shops, and pilot transition training are more readily available.
What the original poster may be underweighting is the value of the 182's higher gross weight certification and its more forgiving useful load in high-density-altitude or full-fuel-plus-baggage scenarios, along with its reputation as a more capable short-field and backcountry hauler when equipped with STOL kits—an area where the O-470's torque characteristics and the airframe's stouter gear and wing loading show real advantages over a converted 172 despite the horsepower being nominally similar. Additionally, the 182's constant-speed prop as a factory-standard feature means airframe-engine-prop compatibility and documentation are cleaner than aftermarket STC'd 172 conversions, which can complicate insurance underwriting, resale, and maintenance sourcing depending on which conversion (Texas Skyways, Air Plains, etc.) was installed and how well it was documented. Insurance considerations, STC paperwork continuity, and maintenance shop familiarity with the specific conversion are exactly the kind of due-diligence items that separate a good used-aircraft purchase from a maintenance headache down the road, regardless of airframe type.
Broader trends in general aviation ownership continue to push toward exactly these value-conscious calculations, as rising avgas prices, escalating parts costs, and a tightening maintenance technician workforce make total cost of ownership the dominant factor in light aircraft selection, more so than raw performance numbers. The interest in horsepower-upgraded 172s reflects a wider movement among owner-pilots toward maximizing utility from smaller, simpler, more parts-common airframes rather than defaulting to the next size up, a trend also visible in the popularity of Cessna 180/185 conversions, RV-series homebuilts with fuel-efficient four-cylinder engines, and the broader used-aircraft market's premium on documented, well-maintained STC modifications. For flight departments, instructors, and charter operators alike, this thread is a useful microcosm of the acquisition logic that scales all the way up the aviation food chain: performance parity often matters less than acquisition liquidity, parts commonality, and predictable maintenance costs over the ownership life cycle.