Mechanically? Doesn’t matter. Not a factor. Why? Each part replaced means you do not have to replace it again for a while. Example: If you just replaced your alternator after 200,000 miles, that means that alternator is good for another 200,000 miles.
Even new cars sometimes need the same mechanical repairs as a car with 300,000 miles. Just depends on the car, but theoretically, that part will not need to be replaced for sometime.
The only time you should replace a car, especially for rideshare is if it has severe cosmetic damage. (gets in a car wreck and it gets totaled by insurance company)
When it ages out on the rideshare platforms. But at this point, you should strongly just consider deliveries as Uber and Lyft will continue to lower the rates. Take Las Vegas for example. Some drivers are now getting paid as low as 24 cents a mile. That does not justify getting a car on payments that will drastically decrease in value over the term of the payments. You can, and you can probably pay it off in due time, but it will drastically eat into your profits. It is not the wisest business decision.
If you are able to, take the down payment you would of and buy a cash car. This way, you can have a backup just in case yours takes a couple of days to repair. In Houston, Uber cars as old as 15 years old. You may miss out on Lyft since now they require 2015’s and newer, but do not let that influence your decision. The one making these drastic rate cuts is Lyft. Why? Because they know a 2015 or newer at 60 cents a mile is not doable. They want you to drive that Express rental for even less money! So keep that old thing running until someone hits it!