Whatever takes your fancy, as a 'fun' car is very often an extension of the owners personbality etc.
I have loads that I want to do to my car, but time, space, cost and not least skill are all factors. I bought my car as a second car for me. My daily driver is my trusty Passat TDi estate that has done 140,000 miles in just seven years and does everything that I would not want the 911 to do.
I am not saving my car for anyone, nor do I consider it an investment. An interesting analagy is when one of my staff asked how I could afford to run a Porsche ? I replied "How can you afford to throw away £300 a month on your new Mondeo!". My 911 will pretty much always be worth what I paid for it, and therefore any money I put in to it is purely for the hobby / fun / interest of it.
I would like to track / hillclimb the car, but also want to use it for regular road trips. Therefore, sensible modifications to the brakes, suspension, steering, interior will achieve this, without changing the BHP or gearing in any way - that way it will be suitable for me. If the next owner wants to return it to standard (as Andy said earlier), or indeed tune it more, then good luck to them.
So I say, do your own thing, but most of all enjoy your car for how you want it.
Just my 2p worth.
And finally, so that RB doesn't wear out his copy of the picture, this is how I would like mine to look :-