Let's start with a look at cars in general... any car, exotic or otherwise is about compromises. That is, in order to do something well, it must compromise something. For a car to perform well it will trade things like fuel economy, at least some level of comfort, storage space, ect. High end exotics will also trade affordability in order to be more exlusive as well as to have a larger budget for things like chassis development.
A high end street car that is mostly aimed at performance is still not entirely aimed at performance though. A car like the Veyron is very fast, but in a speed contest it has fairly major flaws as it was designed to be a street car that provides ALOT of comfort... so it's very heavy. A car like the Lamborghini is designed mainly for flash, and while the most recent examples are better, they are still often lacking in the area of chassis devleopment (and are certainly not a competitition platform). And cars like Ferrari or the upcoming McLaren are developed at least partially from competition experience and have at least the basis of such a car, they are nonetheless very compromised in order to meet the expectations of owners that will be driving these cars on the street.
So, with that out of the way... what do you mean by a "tuned car?" If you take a car that is a decent enough of a platform to start with, and then do away with anything that compromises the performance (ie, full race suspension, racing tires, remove all weight like padded seats, stereo, AC, etc), you will have a purposeful car that will perform much better in a speed contest. It's not a car that you would want to drive on the street or be stuck in on a hot day in traffic, but it will perform!
So the real question then becomes, when saying a "tuned car," what kind of platform are you starting with (ie, chassis balance, rigidity, and starting suspension pickup points being key), what are you willing to compromise (is this to be an all out race car that will compete after being towed to an event and is expected to run a few hours and may then need a complete rebuild, or is it to be a daily driver... or just where between those extremes), and maybe most importantly, what are you willing to spend to get it there (are you going to use a stock engine or spend $50k+ having it built, do you have a team of engineers to custom fabricate new sheet metal to push the project along, etc).
If you start with a Honda Civic, add 200# of stereo weight, a rear wing, and an exhaust with a 4" tip, you can expect a car that will perform roughly like a stock Honda, but with more weight, and no where's near what a Ferrari or Bugatti would do... if you take a Miata or similar car with the right chasis and go all out, but still run a stock engine, you'll have a car that exceeds those exotics in the corners at least, but will fall far back when the straights come as it has but a quarter or less the power of those other cars... and so on.
The amazing feat of the high end sports car isn't just the outright performance, it's the level of performance that is obtained in a car that is at least a moderately comfortable street car, that will not stall or overheat sitting at a stop light, or burn through spark plugs every day. The compromises it makes are very slight in contrast to what it would take to overcomes these in performance, but it certainly can be done.