I wouldn't start using oil additives til 150,000+ miles on the engine.
I've only used Lucas heavy duty oil stabilizer in one older vehicle (1994 Jeep Cherokee) that was owned by a girl that didn't know the importance of an oil change. Checked her oil, there was none. Changed her oil and when I drained what was in her pan, it was like mud oozing out in slow motion. Actually it was mud... She left her air filter cover unfastened for unknown reasons and lived in a dry, sandy desert. I replaced her air filter and discovered a pool of oil in the bottom of the air filter box and large deposits of dirt and sand just trailing into the intake orifice. Needless to say, we all know what will happen to that engine soon. I just pray she wont break down while she is out in the middle of the desert by herself.
That's the only oil additive I've ever used in a vehicle. I use Lucal fuel treatment a few times a year to make sure the fuel system is healthy. I had engine issues a few times that were caused by not driving for months at a time when work flies me all over the place. Gunked up fuel systems sometimes cause stalling, bad idling and unreliability. One bottle and a full tank of Premium seems to do a GREAT job at cleaning.
My buddy worked for an engine oil company for a few years. I won't say what oil this is... but they tested it unchanged in an engine for 100,000 miles and analyzed the engine condition very thoroughly and discovered that it could be compared to the same engine that had regular interval oil changes and oil filter replacements. He swears it's not a joke and he personally has driven 70,000+ miles on two different cars that use this oil and hasn't gotten an oil change. The down side is this company sells the oil for $35-$45 USD. per quart. I won't ever go more than 3,500 miles without an oil change. I try to stay within the 2,750 limit the manufacturer recommends.
Yeah, I rambled a little. The best thing you can do is just keep up with your oil changes.
Does anyone remember the old STP Oil treatment? It was a can of very thick stuff like molasses/honey. I'm fairly certain it wasn't good for most low mile engines, but it really quieted the old noisy valves in older ones. It was great to pour in the engine before you sold your old car. Now, how about the old Arco Graphite oil. That black stuff made a complete mess of the engine inside and took a few oil changes to get it all out. Not sure if it did all it was supposed to do either. I wonder what would happen if one used Wesson cooking oil in their engine. It would have to work for a while before starting a grease fire in the engine compartment.