Should I continue to invest in my 2006 Prius?

Can you do any of the work yourself? If the answer is no then it might be time to buy a newer car. The Combo meter is not that much if you can do it yourself, or see Matt in Dallas.
Prius Speedometer Replacement
However you probably need struts and will need a new battery sooner or later. Plus the abs module is always a possible failure also.

 

125 is low, but as ski says above, you could be in for five to ten thousand dollars of work in the next few years if you rely on a dealer

 

Skibob aka Ski or Bob?

 

Don't forget that age-wise you are due for replacing the hybrid battery. ~$2,500-$3,500.

Keep an eye on oil consumption in case it starts burning oil. You don't want it to get too low.

The combo meter final failure is pretty random. It may completely fail this week. It may completely fail 5 months from now. Now matter when it does, it is always at the most inconvenient time. (On the way to a job interview, on the way to Grandma's in a snowstorm with the kid in the car, etc) .Take care of it now.

 

KEEP: able to DIY, car well maintained and NEVER let the oil run low causing warning lights to appear.
SELL: you have to pay for labor

Impossible to predict what will go out next and when. This would make keep/sell decision easy. As everyone has pointed out, future failures you can count on are: HV Battery, ABS modulator, and possibly AC issues down the road. Remember, you keep anything long enough that is used regularly, components will fail requiring repair or replacement.

Should you decide to replace the front struts and rear shocks, I would avoid the quick strut/shock replacements; but that is just me.
Read post#13 for pricing of strut and shock parts, to give you an idea; keep in mind pricing was from 2015. Additional Front/Rear Strut Replacement Parts Needed Too? | PriusChat

The strut/shock manufactures (KYB, Monroe, etc) all recommend 5yr/50,000mile replacement intervals to maintain OPTIMAL vehicle handling and braking quality. I replaced my after 7years/127K miles. WAY OVERDUE! No visible signs of oil leakage from the struts and shocks. NO visible signs of odd tire wear (ie hopscotch marks). Ride seemed normal; but makes sense that you get used to the deterioration over time since it is slow and you have nothing to compare it to.

Only when the old struts and shocks were removed and compressed by hand, and compared to NEW, was the degradation obvious.
NEW front: 7 seconds each. OLD right: 57sec. OLD left 18sec.
NEW rears: 7 seconds each. OLD rear: 3min 15sec for one. The other one, way longer, and stopped timing; eventually it did fully extend.
As you can see the rear suspension was essentially only spring, and hopscotch marks on the tires would be expected. But was not the case.

 

Mine is coming on close to 200K miles. My combination meter did slowly go out. The worse part was parking and either taking forever to turn the thing off (when the meter went out, I often had a hard time getting the car to turn off). Sometimes so getting upset with it I would wind up leaving the car on in a public parking lot - because i really had no choice. Don't go though that aggravation, get it fixed ASAP. The car was garaged kept all its life, and often in a parking garage when I went to work - so well taken care off. Never seen snow, always a florida car. I wound up fixing it using this thread -

combination meter repair - DIY | PriusChat

This requires soldering very tiny parts, and working at an electronic manufacture company I had access to people that could do this for me so it was a slam dunk. Worked great ever since - should have done it sooner. Or, change it out as recommended by Skibob.

I have no idea how well taken care of your car is, but for me and my car I've had to do very little to it up to this point. The combination meter, and AC, accessory battery (that was another weird issue kept stalling on the road randomly), is about it. Hybrid battery, cooling pump, etc.. All original and car runs great. But like any used car, you never know what's around the corner... I'll pour a bottle of champagne over her when she hits 250K miles.