The original performance Pontiac market is a wide spectrum, beginning with the Trophy 389A*Catalinas & ending with the last of the traditional Pontiac engine T/A's, near twenty years later. With a lot of Chevy drivetrain cr#p Fbodys being built in the 80's, the continuation of the original era died, & the later performance segment leading F-bodys & late Holden/GTO's have their own markets.
The original era ('64-74) GTO market is a subset of the wide '60's -70's performance Pontiac spectrum. Within that subset, the high price setters have consistently been the very desirable color combination, highest performance models, either restored to the very highest exacting detail, or as extremely clean low mile highest performance model original examples, each avenue has commanded top values. Everything else has trailed in price valuations! that includes what Jim has referred to as "Toys", another segment which consists of the local show car / occasional driver. To not acknowledge the segment price leaders being investment grade muscle cars is naive. not all can qualify for such a label, but when values rise, the segment leading investment grade models tend to pull the rest of the pack up in valuation slightly.
The above noted, anyone who has been very active in the performance Pontiac market can convey the contemporary day owner modified/ "modernized" vehicle is no where near the standard bearer, price wise, in any of the performance Pontiac market segments. For those that believe they can through their own capabilitys, streetrod build the rarest & most desirable original GTO or F-body models, spending serious funds, to have a vehicle that stands out while having the ability to handle & perform at a level they feel is comparable with late model muscle, that's all fine & good. it's your money, but selling prices on such cars are not bearing out anywhere near the market average for same year highly desirable highest factory performance GTO's in what many would consider even #2
condition. Modifying much less rare models, saves such inclined "builders" a high entry price, but does not guarantee, when needed, original parts will be more affordable.
As a modified Pontiac, the only market segment price leaders have been a few factory race cars that were modified by Pontiac Engineering & subsequent purchaser. The previous Randy Williams owned/Tieman restored Union Park '63 Tempest wagon & the following '63 LeMans Coupe are fine examples of their own body styles/models. https://www.supercars.net/blog/1963-...21-super-duty/
One should note that these '63 Pontiacs have been restored to as prepared to race in 1963 They are not a creation of the builders imagination, a recently compiled array of "Day 2 parts", or the cultimation of a spending spree of hot ticket items presented at the last SEMA show or hyped in magazines, websites, or contraption "building" cable TV show.
Back to the OP's '65 GTO. Nowhere has he noted the factory options his '65 GTO was built with, or the factory color combination. Also not noted is if the GTO is still that color combo, & most importantly, an accurate summation of the vehicles condition. All help determine desirability & value. A good percentage of nice driver condition local showcar early GTO's typically fall into the mid #2
condition car. Many would agree the best way to convey value is to watch the money change hands on the sale of similar condition same model vehicles, that may be through trusted shared information of a private sale, or through auction results minus seller's fees. Insurance payoff mean little.
As far as auctions go, no reserve auctions are a double edged sword, many times, what a seller believes his/her vehicle is worth just doesn't come to pass. On the other hand, occasionally, there will be an event where there is a massive run up in prices, yet in the end run, the hangover is temporary. In the late 80's-early '90's, there was publicized the high gavel prices of several persian sand colored '59 Eldo Biaritz converts. Lot of hype! Later it was revealed, a group of several owners were bidding on each others '59 Biaritz converts to create the illusion of high values... what a deal! More recently, in Jan 2014 @ BJ, there was the craziness & circus atmosphere of eleven '69 RAIII Judges being presented through out the auction for bidding. All gaveled at very high prices for their actual quality of restoration/condition. A few month later, printed & online "Value Guides" parroted the rise in price "values" of the '69 Judge model. In the real '69 Judge owner/hard core restorer/enthusiast community, most realized the comedy of the BJ sale of those particular cars. Any other year, any other BJ auction, there was no way such condition "restored" Judges could bring that much money. Unfortunately, such results are not filtered into the publication of such "Value Guides". At the same time, many private sale prices are seldom factored in either.
In considering selling the '65 GTO, only you know your health, revenue streams, expenses, & what makes you happy. If you feel that it's time to sell, none of us have a crystal ball. For one, I don't buy into comparisons of the market of original Pontiac era muscle car to that the market of Tri-Fives, not as a longtime participant in the performance Pontiac market, that said, I'm not a member of the local musclecar cruiser bunch/lawn chair crowd. Neither are the majority of longtime Pontiac restorer friends & collectors.