Oil change for my 90 LeSabre

Hello everyone, I've been using Valvoline Maxlife in my car for about 20,000 miles(changing every 3,000), and I'm wondering if it's ok to switch to a conventional oil. The oil change shop in the area is now charging over $40.00 for a Maxlife oil change compared to $20.00 for the conventional. Am I wasting my money with the Maxlife or should I just switch. I have about 150,000 miles on the 3800 and plan on having the car for a while. I know I should be changing the oil myself, but I don't have the time.
Thanks!

Leo
1990 LeSabre

are you burning any oil between changes? how black is the oil when it comes out? This time around, I'd check those things out, if none is burning and its not bad black(trust me, you'll know) with a funny smell, the engine is in tip top shape, and conventional oil is fine. In nearly all cases, conventional is fine too, so I'm giving the greenlight on your oil switch, but do please answer my questions.

I don't really burn any oil at all between changes, however, the oil is dark but doesn't seem to smell. It sounds like conventional oil would be ok then. I know a lot of oil change stations use a "cheap" or generic oil, are these less protective than "top shelf" oils? Just curious...Thanks!

Leo