You're right maintenance is a big deal. If they took care of it, they should have the records to prove it. A rig that has been sitting might have few miles, but it may also have developed some issues from sitting and neglect.
I did not see any Jaycos when we were were looking. As for build quality, barring a luxury motorhome like a Foretravel, Winnebago was undeniably the best made. A big plus for Winnebago is they archive their manuals and schematics. You can download pretty much any information you need. And parts for Winnebagos of that era seem to be readily available.
Here's a couple Minnie Winnies close to that year that have sold on ebay:
1998 31' 23k miles $15,500
1998 31' 34k miles $12,900
I don't know if Jayco has that front window over the cab -- the one in the bunk area. If it does, check the area around the window inside and out for delamination. They are prone to leak.
Good luck with your search. Don't be afraid to ask questions about everything. There's a pretty good bunch on this forum.
Oh yeah, watch out for delamination on the sidewalls of any rig you're looking at. That can be prohibitively expensive to fix.