If your car was starting to have a lot of mechanical issues (see details), would you go for repairs or buy a new or good used car?

My 2002 Honda Civic is suddenly having a lot of problems - SRS dash light always on, AC doesn't work, squeaking and thumping underneath on front passenger's side and brake pedal, and passenger side mirror is loose.

You can repair a car up to a point, but there comes a time when you're just throwing good money after bad. I usually get rid of a car when it costs more to repair it than I could sell it for.

I had a Mondeo that was 11 years old when I bought it for £650. It lasted me 6 years & had a perfect engine that never went wrong, but I had to replace it when the bodywork just started falling apart. I now have an 11 year old Vauxhall Zaphira.

Cars are designed to fall apart. Nothing's made to last these days. That's how manufacturers make more money out of us.

Do you have a good independent mechanic? If not you need to find one.
Have them evaluate the vehicle and give general opinion and some specific quotes on fixing some of the issues you listed. The AC could be one leaking hose, fix that and it might work. Or the compressor is bad, but you can find used compressors or aftermarket ones that may be ok price wise.
The bakes, loose caliper or pad?
Key points to evaluate first. Engine, running OK, burning oil. And headgasket leaks or major oil leaks.
Is Transmission OK, most likely needs drain and fill, then come back a week or two later for a drain and filter change. Body - are there rust hole and rust on the frame and under body that is not fixable.
Cooling system - corrosion and not working right. And last is timing belt, is probably past due.
If the core systems are OK, then you might be able work through the other issues like one every other month.

Or if you can afford it, upgrade to a used car in the $10,000 to $15,000 range and sell the CIVIC as is for what ever someone will pay. It depends on your budget. Going to a 2005 Civic, depending on the miles, may be a better car, but any car in that range will also need work from day 1.

That all depends on the relationship you have with your local workshop/mechanic. If you have on you can trust to do what needs doing, properly and at the right price. Then repair until the engine or transmission develops a major fault or the bodywork starts falling off.
Otherwise start looking for a good low mileage replacement at a price you can afford. Don't buy anything until a reputable, independent mechanic has checked it over.

For a very obviously non-mechanical person like you who can't even attend to a simple thing like loose mirror, a newer car without any issues would be a better choice because the labor for repairs costs $100 per hour and up. I'd say you're easily looking at $1500 in repairs or more.

Unless you can afford the high payment, tax, registration and insurance on a new one, I'd look for something about 4 years old with low mileage that still has some warranty time on it and the biggest hit in depreciation has already occurred.

Those problems are relatively minor. As someone who loves messing around with beater cars, I would continue to drive it. AC systems generally have issues within 5-10 years. I would be too lazy to fix it unless I can determine that it isn't going to be a money pit. This is from someone who just has to have his sh*t box. Someone like you would want to call it quits.

That is precisely what happened. I knew I was going to have to replace the radiator, I had developed a serious crack in my windshield, and there was paint problems starting to develop. I had been watching the local market for cars and one came up that was right in my budget. Combine that with the government incentives to move up to a newer (read: less polluting) vehicle, and it was a no-brainer to replace that older car.

I don't know…

That was one of the worst years for a Honda, and those problems are very common for it. The most serious faults is transmission failure- they last about 30,000 miles and fail. Get rid of that old dog.

Go for repairs

Pay for repairs or pay for a monthly payment and possible car repairs.