First thing is to use the right oil, since the oil change interval assumes you're using the approved oil. For several years GM has specified the use of oil meeting their "Dexos" spec, which typically means a full or semi-synthetic oil. Not all oil makers submit their products for Dexos approval, since it costs them money, so most full-synthetic oils are probably satisfactory even if they don't have the Dexos label. I am not aware of any non-synthetic oil that has been certified as Dexos. Looking at the list of Dexos1-approved oils, Pennzoil makes several approved full and semi-synthetic oils.
As for the oil change indicator, I'd say it's very good if you follow it religiously. If you're in the habit of ignoring it for several weeks, then you're probably not changing your oil often enough. Be honest: do you REALLY change your oil every 3000 miles? Or do you start to think about scheduling an oil change when it hits 3K and maybe get it changed around five or six thousand? I drive about 3K a month; no way am I going to change my oil once a month.
I am told by some folks who should know that the oil change indicator algorithm doesn't necessarily account for trailering. This is of particular concern with some of the vehicles that have very long oil change intervals (such as the 4.2L Trailblazer, which seems to go around 14K); if you do a lot of trailering it makes sense to go with a more-frequent oil change interval. I doubt that's an issue with your Buick.