If you are asking it as a way to make money--a GT6, no, they are just not worth it on the market, if you do all the work yourself and don't count your labor as cost you might be able to break even or even turn a small profit depending on what you need for the car, but if it needs an interior, chrome, paint, mechanical repair and rebuilding and I assume it needs most of these if not it will be a hard proposition to make bucks.
If you are asking is it worth it to buy because for whatever reason that is the right price point for me to buy the car now, I have always wanted a GT6 and I like to fix up cars it can be a good and enjoyable purchase for you and a sound personal investment.
As far as making money on cars at the lower end of the collector car market if you can buy them from people that have a decent car, but don't have the time skills or inclination to make some minor repairs to make it right and you do there is some possibility there. Case in point freend who bought a non running MGB GT, he suspected fuel pump it was and a $500 car went to a $1000 car for basically nothing, he just filed and set the points. Otherwise for investment purposes you are better off going to the higher end of the spectrum, Big Healeys and Jags come to mind, but the price of admission is much higher.