OP though I've not tried the GTS - as ZermattV has mentioned I've had my '12 Boxster S for a few months now and it has IMHO all the important driver focused specifications such as PASM ( love it though the Sports threshold is very firm and probably suitable only for track or very smooth roads), Sports Chrono ( looks cool & fun but the actual usability is a little questionable - I probably need to explore further though combo of PDK and SC gives some more features), Limited Slip Diff which I'm pretty sure I've felt push me round some bends, Porsche Torque Vectoring - love the idea of aiding traction and increasing cornering speed but not sure if I'm sufficiently skilled yet to notice much and no idea if you feel the LSD or the PTV ??
Switchable sports exhaust is awesome - I negotiated this with the OPC as part of my deal with no trade in etc. It's useful to be able to switch off at times as it can be loud if you're behind someone you would rather not accuse you of loutish behaviour or pootling through a village. When you get a chance to open it above around 3,600 and hear the sound bouncing off both sides of a bridge maybe it's wonderful - I've not been near a tunnel lately but looking forward to that.
Also have adaptive xenons, cruise, PDK, launch control ( tried that at Silverstone in their car !!), PCM etc. so it's difficult to see where the extra is for the GTS unless you love Alcantara - I don't - had it before in a my daily driver, an Audi and wasn't impressed how it wore and bobbled. Extra power in GTS is only 15 bhp which you could get from a re-map if you must but doubt it makes much difference really.
Sports & Sports Plus buttons make a very real difference particularly to throttle mapping and both gear shift times and shift points - much much more than in my Z4 E85 with SMG (admittedly much older technology). Sports Plus is a bit mad left to it's own devices but pressing on and putting PASM back to normal and even with PSE off it's quite a ride - there's just so many set up options with PDK/ PASM /SC etc.
So - of course I'm entirely bias but I think a Boxster S with PDK, PASM, PTV, PCM, PSE, 20" wheels and a few more acronyms makes more sense and is somewhat more affordable ( still need to use a healthy does of man maths mind to justify it as a weekend car which mine is)
Prices for GTS seem very high and likely to remain so - it is an awful lot for a Boxster I think and that's from someone who genuinely wanted a mid-engined Boxster over a rear engined 911(for now).
Hope this helps.