Welcome to the forum Ol'Timer!
Well, you have pretty much covered it. There are a few other things you could do, but it depends on your wrench saavy. I would definately replace the spark plug wires. Taylor makes a good set that you can pick up from the GPStore (on line--check the links section). This in not difficult at all to do--just do one at a time.
The second thing you could do is clean your throttle body. This is a little more involved. It will give you better fuel efficiency if it currently has carbon deposits in it. You should also be getting around 26-32 mpg on the freeway. If you aren't, you may wish to change your O2 sensor.
As for the 3800 engine, it is a series I based on the Buick 3.8--the same as in the Bonnevilles of the same year. You should have no problem finding stock parts for this engine. Performance parts are a bit more difficult to come by as they are mostly marketed toward the series II engines.
When GM went with corporate engines in the U.*., they selected the Buick 3.8 as the corporate 3.8/3800, just like they selected the Chevy 350 as the corporate 350/5.7 L because they were very reliable and easy to maintain.
I hope this helps out.
Retired Moderator, The Bonneville Club www.bonnevilleclub.com
RIP Oldsmobile, April 29
1995 Bonneville SE Supercharged (Stock)
Current Mods: Dirty GYM Sock air freshener.