1st Time Prius Owner - What Should I Know and What should I Upgrade?

I'd go with safety upgrades first. Inexpensive upgrade, replace the wimpy meep meep horns with better/louder horns (there's a link in my signature below).

Then upgrade the weak lowbeam headlights with either H9 halogen bulbs or HID.

 

I wouldn't touch it! I gave myself a "maintenance only" policy on the '07--no mods!. I have the '85 truck for tinkering.

IMO, there isn't really anything you can change that is cost-effective and would produce a noticeable difference, without sacrificing qualities like reliability and fuel economy.

 

I have had a great time modding my Prius, using the JDM G-Sport as a guideline. I've got big improvements in performance handling and aesthetic appeal. But all of that comes at the cost of fuel economy.

If fuel economy is your chief concern, then I am with @tanglefoot on this one. The best thing you can do for fuel economy is to leave it bone stock. Don't upgrade the suspension, don't change the wheel/tire specs, don't add a throttle controller. Even if any of those mods don't directly affect gas mileage, anything you do to improve the performance of the car will beckon you away from efficient driving techniques.

If fuel economy is a secondary concern, then you could find some middle ground. You can have sports car handling and good looks with fuel economy well beyond any sports car.

That being the case, I suggest a Cusco front sway bar & strut brace, TRD rear sway bar, and TRD springs, along with some 17" or 18" wheels with a good set of performance tires. Those mods will flatten your cornering, like nobody's business. For a little extra umph, put in the APEXi throttle controller. Then it's time to start on the aesthetics. How about a shark fin antenna, rear wiper delete, a roof spoiler, LED lighting (interior & exterior). If you're in the mood for some swanky upgrades, go for some auto-folding mirrors, and a high end HID retrofit. Throw in a new Android 4.4 head unit and a Real® leather steering wheel, a set of premium JDM horns, and some projector fog lights. Then it's time for a G-Sport body retrofit! But that's just me.

 

Minnesota? Block heater and snow tires.

(Basically: everyone responding, myself included, is gonna tell you stuff they've done to theirs, or wish they had. Nothing wrong with that, just you have to take it all with a grain of salt. Road salt??)

 

If it were mine, I would change the ATF WS in transaxle now, at 90,000 miles and then every 90,000 miles. I think that will flush out metals that can short circuit the Motor/Generators, which are cooled by the ATF.

No cheap or simple mods will give it more horsepower, although a different intake or exhaust can make it louder, which might convince you it had more horsepower. Ride improvements come at the cost of handling and gas mileage. There are better riding tires, they just are not Low Rolling Resistance. Keeping the air pressure stock will ride better, but handling will suffer, as does gas mileage. 15" wheels seem to get 3 MPG more than 17".

Michelin Premier A/S

 

Learning how to hypermile a Prius will be way more effective than buying snake oil.

Study all you can about pulse and glide.

 

There is no "performance chip" for the Prius.

But there is the APEXi throttle controller:
Amazon ASIN: B007ZDR8FA
Amazon ASIN: B008JO1ECM

This product gives you a wider range of throttle settings that go beyond what the Eco & Power buttons offer.
I tend to run my in RED mode when I'm in commuter traffic. Or when the atmosphere is more relaxed, I'll put it in WHITE mode for super smooth "eco" acceleration.

What did you do to ur Gen III Prius today???? | Page 464 | PriusChat

 

upgrade the suspension - see here

 

Be aware that the above mods will improve handling at the expense of ride

 

Block the grill.

 

Engine Block Heater for 2010-2014 Toyota Prius - PriusChat Shop
since you are in MN

 

don't even think twice...DASH CAM! It's saved me twice to date. Check the wire cutter for some reviews. I purchased an additional fuse kit, from the dashcam store, to make things clean. Just make sure to double check if you need a mini or micro usb connection.

DashcamInstallation Kit - 5-Volt USB Plug - Low-Profile Mini Fuse
DCSIK50

 

The iJDMToys interior kit is super bright and totally easy to install.
The other cheaper kits give you LED light at about the same intensity as the OEM incandescent bulbs.