Are Gumout additives recommended or should I get a tune up long term?

I've used Gumout additives in the past on my 91 Accord. And I find that they generally do work. The car will start easier, shift smoother, and get better mileage. Although the first time you use it its usually the most pronounced. On the package they recommend every 3K miles. I find that excessive and even my mechanic at the time said at a maximum every 6K if that. And that is about what I did. I would usually use one every 6-10K miles. I didn't really have a system down for it. I would just use it when it started getting to the point of shifting fairly hard between gears. Anyways, now I have a new car, 2007 Nissan Versa, and was thinking of using it on that with probably even less frequency. Some say this can damage a car but I find that unlikely due to the frequency and the mere fact is available all over the country. I imagine in an excess it probably could though. But I was also thinking of getting a tune up, probably before winter, since I get the impression that the guy I bought the car from didn't take much care of it. He did the basics like oil change and fluid top off but was too lazy to even wash the car so somehow I doubt it has had a tune-up or things like that. Granted it only has 53K miles so it shouldn't need much. But thought it might be a good thing to do in the next couple of months as a new owner and all. Any thoughts or suggestions would be appreciated, thanks!