Hey, turns out if you take head west on Harmon Ave. and cross Las Vegas Blvd., it will take you directly to the parking and valet entrance for the Cosmopolitan. When you leave, turn right onto West Harmon, turn left when you get to Polaris, and you'll come out on Tropicana, just west of your choice of I-15 or Dean Martin. Avoid that nasty Strip traffic altogether!
If you don't upgrade to a terrace room...well, you get very little of that stuff. You will get a very nice good-sized room with comfy beds which will likely have a spectacular view and overlook the pool. You get one decent-sized flat-screen TV. There's no kitchen; there's not even a microwave or a coffee maker. There's the fridge for the mini-bar, and the staff will volunteer to empty it if you want to be able to use it as your refrigerator without worrying about nudging a bottle of champagne and having it billed to your room. The extra roll of t.p. still comes in a draw-sack, and you might still want to draw those blinds. Also, all the Cosmo's rooms are non-smoking, so if there are any smokers in your party, they might really miss that terrace.
So is it worth $40 to upgrade to a terrace room? Hell, yeah! If you can get a good deal on a room at the Cosmopolitan (like, only being charged the $25 a day resort fee) for just one or two nights, you should treat yourself to the experience at least once. Careful, though; you might get addicted to it.
Heads Up: By default the Cosmopolitan will put a hold on your credit card for $150 each night against expenses that might be charged to the room, so be sure you have that kind of funds available.