Here's my two cents.....
I have owned a number of kit cars and did actually use one as a daily driver (Lotus Super Seven) but in the end my, at the time, girlfriend was whinning about getting wet when it rained and the loud noise it made etc. so I had to move on to something a bit more civilized (Lotus Elan) although technically it is still a kit it was equipped with some luxuries...windows (power at that), doors (always a good thing), radio and trunk space.
Even then with all these types of cars I do believe, although simple in concept, they still require more than average maintenance. Don't forget that most are designed and are direct copies of race cars and therefore end up needing more attention as they are built to be rebuilt, if that makes sense. Although some have made significant improvements for road use they can be somewhat temperamental, you only have to take a look through the threads on this forum to find this out, i.e. overheating issues, carburettor problems, fuel pumps problems, transmission issues, electrical bugs and so on. If you are willing to accept that you may break down from time to time and you may need more frequent visits to a mechanic, if your not so mechanically inclined, then OK...but it also won't be cheap, you need to go to someone who specializes in the type of car you're thinking of purchasing and it could still run you $100 plus per hour.
Also, a GT40 doesn't have a spare wheel and no roadside service is going to have a knock off wheel and tire handy.. I know you can get a can of slim to temp fix a flat but it doesn't work all the time. Also, you mentioned gas consumption as a concern...well I don't think there's many GT40 owners that probably give that any consideration and I'm guessing that they don't get much more than 15 mpg at best, I know I don't but maybe that's just a heavy right foot
.
Most GT40s have some kind of water leak at some point around the doors. I know the sound inside the car is awesome, but I don't think there are too many of us who would feel that way if it was a daily driver and neither would the neighbors.
If you want to be noticed and get reasonable gas mileage and have some form of comfort I would look at something like a Noble that is a more refined, high tech, hi power engine, comfort etc.
Despite what you might think now being in awe of the GT40, although it pains me to say this, I think making it a daily driver will wear you down. I would think long and hard about making any of these types of vehicles a daily driver. You really need to be around them and understand them for a while before making that leap unless you can afford to park it in the garage and go out and by another daily driver.
Not really trying to dampen your day......just think carefully before you leap...
Cheers,