I'm planning to trade in my car on a newer model. My decision to go ahead and do it soon was based on the fact that I had several expenses and maintenance tasks coming up soon: registration, tires, flaky AC. For a trade-in, what kinds of maintenance and repairs generally make economic sense? Is it worth my trouble to remove my political bumper stickers? To get the interior professionally cleaned? To replace the tires or fix the AC? We're talking about a 2010 Honda Fit with a bluebook value of about $3-4k.
Honestly, don't do it. The ROI on doing maintenance before a trade in is negligible. Most dealers don't car about the tires on the car as long as there are tires on the car and they are not dangerously bald. Things like making the car look nice might add some additional value, but again the ROI would be low.
If you really wanted to see if you can negotiate a better deal for the car, bring it in as it and ask how much they would give you for it. Then ask how much would the give you for it if you did such and such. This would give you an idea which maintenance items are worth it.
The only time it's worth putting money into a car to trade it is if the money you get is more than the money your spend. If you have a car that's not running then getting it running makes the trade in value much higher, so can be worth it depending on how much it costs. Other than that, cleaning a car so it's not filthy makes sense but not paying for it to be professionally detailed. Putting new tires on costs you lots money but won't get you anything more on the trade in price, because the dealer can do it cheaper than you.
The most important thing is to know what your car is worth as a trade-in and be prepared to negotiate for it. Dealers will often give you a trade in far below value to maximize their profits, so know your stuff and be willing to stick to your guns.
Among everything you said, i would personally fix (and also tweak: things such as AC line soundproofing so you don't hear the compressor inside too much, and condenser external cleanup+radiator/condenser gap sealing with foam, things i've successfully done on my car myself) the AC, then show the compressor working correctly and then the cold and heat the AC system can provide inside at request. You don't know how many cars get sold with the "AC just needs regassing" trick that then turns out to be a serious leak (such as a leaking evaporator), a seized compressor or an inoperational compressor clutch, so keeping AC in top shape and then showing that to the buyer might definitely be added value.
Yes, your "flaky AC" might range from a simple cabin air filter replacement & regas to a seized compressor or evaporator leak, but in my own opinion it's definitely worth looking at.