There may be a bubble forming, but often bubbles are just markets getting a little ahead of themselves. I have to believe that the GT has a lot more than just its total awesomeness going for it in the long term.
For one thing, demographics. Baby boomers (who also own many of the GTs) are aging and even though we are trying to spend savings, most of us will leave a lot of inheritance when we start kicking the bucket. Younger generations will be enriched by our deaths. I saw this happening in Germany as the WWII generation, who, like the depression-era generation, were frugal and passed a lot of wealth on to the next generation. Which, to a large extent, is why so many younger people in Germany are driving Porsches and MBs.
For another thing, every generation now living thinks the GT is totally awesome. This is different than the hot rod generation, or the muscle car generation, or the tuner generation. Everywhere I go, teens and pre-teens are schooling their dads (many of whom are clueless, but still awed) on the GT. Kids tell me the GT is their favorite car in car race video games. This is not isolated geographically, culturally, or socio-economically. These generations are going to carry the love of the GT forward, just as us old farts carried the experience of the GT40s forward.
Further, GTs are almost invariably well cared for and, because they are nearly bullet-proof, a high percentage of those not wrecked will still be in great shape in 20-30 years. At which time, they will still turn heads.
And...there will never again be anything like the GT.
So, IMO, no matter what you pay today, in the long term it will be a great investment.
That said, I don't care what happens to the value, because I just want to drive it.
BTW, how do you have half of a bubble?
P.S. $1,700 with Allstate, which also has my home and other vehicles. And no annual mileage limit, which is one reason I dropped Hagerty, which was charging me $3K for 2,500 mile limit. Rates are highly variable based on location.