Age makes no difference, as they were only manufactured over a 2 year period and with the Facelift 4200 that preceded it, they are pretty much identical and well sorted.
The only real choice with the GS is Tech or LE. For me, its always been LE but you get your money back at the end with either if well looked after, even a bit more in this rising market.
One final consideration, I would try and get the Pre 06 models, purely as the RFL is half the price each year and £550 is a lot extra to pay.
You have slightly contradicted yourself there since you will struggle to find a pre-06 LE spec car. BUT it is also important to note that the LE designation was purely an advantageously priced option pack on the later models. So with an LE you know you are getting a well specified car but it is not only LE cars that have full leather and plenty of 05/55 plate cars will have been ordered and built to what later became the LE spec. I know you know this but this is for the benefit of the OP and others searching a GS
Spec and options for UK cars (including the later LE Option Pack below):
Standard:
Skyhook
19 inch Trofeo design alloy wheel.
Maserati Stability Control
Leather and Brightex racing fabric interior (Nero, Grigio, Nickel, Blu metal)
Sports seats
Start button
Deeper front and rear bumpers with chrome front and rear grilles, side skirt under door
Four airbags.
Cambiocorsa model F1 derived 6 speed paddle shift transmission with electro hydraulic clutch actuation and automatic double declutching (35% quicker changes than CC)
Immobiliser and alarm
Three spoke sports steering wheel and centre console in carbon fibre.
Exterior colours - Giallo Granturismo, Rosso Mondiale, Nero Carbonio, Blu Mediterraneo, Gfigio Touring or Bianco Fuji at extra cost.
Nav Track
Sports exhaust system.
Options:
Out of range paint - £1450
Paint colour from sample - £2900
Pearlescent Bianco Fuji - £3482
Coloured brake calipers (red, aluminium or yellow) -£388
External grills in black - £295
19 inch Trofeo alloys - Grigio Mercury - £470
19 inch Trofeo alloys - Ball polished - £755
Cruise control - £341
Spare wheel - £441
Carbon fibre rear wing - £775
Sat Nav and GSM phone - £2465
Auditorium 200 hi-fi - £645
Electrochromic rear view mirror - £235
Xenon and washer jets - £964
Rear Parking Sensors - £447
CD changer Becker six disc - £540
Five piece luggage set - £1721
Fire extinguisher - £341
Car cover - £183
Coloured steering wheel colour on request - £182
Heated front seats with driver memory - £530
Carbon fibre door sill trim - £585
Carbon fibre door panel trim - £495
Aluminium passenger foot rest - £425
Full Leather in lieu of brightex racing fabric - £1680
Packages:
Limited Edition package (LE) - £3175
Red coloured calipers
CD changer
Full Leather
19 inch Trofeo in Grigio Mercury
Electrochromatic rear view mirror
Heated front seats with driver memory
External grills in black
Seatta badges
Xenon headlight washers
Auditorium 200 high power hi fi
Rear Parking Sensors