I have a 75k 2011 IS350.
It's my daily and I take good care of her, but like anything else you get used to, things just get kinda mundane after awhile.
I spent an evening and a few hundred dollars to add some 'spark' back into the relationship....
I'd recommend these updates as worth the $ and and time.

$350 Takeda Intake Install - adding a roar when you punch the pedal is just plain fun...it's there when you want it, and not there when you don't
$70 Denso spark plug replacement
$10 MAF sensor clean
$10 Throttle body clean

 

2010 IS350 Sport, bought it last September at 52K (now has 62K). The only things I've done so far are F-Sport Sway bars, RR Racing LCA Polyurethane bushings, and swapped out the electronic steering ECU for a steering ECU from a 2010 ISF. I don't plan anything else except maybe the RR Racing tune, which will bring the redline to 7300 rpm (I will probably set it to 7K). The car was already fun to drive, now with these simple changes it's a bit more fun with stiffer steering and a slightly stiffer chassis. In a few years I will probably either give this car to my son (he's 16 right now) or sell it and buy a used GSF (I'm leaning towards keeping it)