I sold a small home that I owned and needed to sell quickly by patching the walls and giving the whole home a fresh coat of paint. The exterior could have used new siding but having it repainted was a major improvement. I also added new appliances including a fridge with an ice-maker and water in door and a glass top range. I may have gone overboard but I also added a new washer and dryer and a new evaporative cooler.
I believe the total I spent was about $15,000 and I was able to recover every bit of it and get the home sold. As far as making a lot of money by putting money into the home... that is the gamble. My purpose was to get the home sold and I was able to do that and make a little money in the process. I think had I had the time I could have put a new kitchen in but I am not sure the value would have been recovered at that point. The market where I had my home just wasn't that strong.
Good luck! Definitely compare the homes that are one the market, especially the ones that have sold in the last six months.