We previously owned a 1986 Dana.
There is tremendous commonality from year to year between these boats, so overall condition/wear and tear/maintenance/upgrades would be the most important factors.
That said, some improvements were introduced into the line as time went on. The '86 will have the older style oval bronze portlights, the '98 will have the newer rectangular ones. I prefer the aesthetics of the ovals, but without going into details in my opinion the rectangular portlights are a much superior design.
Around 1988/89/90 or so, a new style electrical panel was introduced. There is nothing wrong with the old style panel, but I find the new style panel has a cleaner and better organized appearance. Behind the panel, the wiring seems tidier also (although, again, PSC is known for good wiring on all their models across the years -- provided owners haven't made too many "improvements"
Also in that same time period, PSC introduced vinylester resin into the hull laminate. This type of resin provides much superior blister resistance. The older polyester-resin boats, like virtually any boat made with that resin, could experience some blistering. We had a few dime-size little ones on our Dana hull. They were no big deal and easily dealt with.
Beyond that, I would look at which optional features the boat includes. There was an option for a second water tank in the port aft cockpit locker. In the '86 time period, kerosene stove/ovens were standard, with propane an option. The propane option added a propane tank locker at the aft end of the port cockpit locker. If the boat has both the second water tank and propane options, that locker will begin to get tight. Later boats all went to propane as standard.
Other options on deck include double anchor rollers at the bow, and a third anchor roller at the stern with its own through-deck hawse hole and rode locker. Roller furling, cutter rig gear (forestay, staysail, sheet lead tracks on the coachroof, sometimes running backstays) are all expensive to add later if the boat doesn't have it.
Belowdecks, it's nice to have the optional cabinets outboard of the settees, at leas ton one side or the other, anyway. Also, there are some fold-up counter extensions that are nice to have too. AC shore power is very desirable, our boat even had "shore water" hook-up.
Refrigeration is handy, but I would hope to see a battery/charging upgrade to power that. Our boat originally had 2xGroup24s with a 55 amp alternator. We upgraded to 2xGrp31s with an externally regulated high-output 70 amp alternator, with a smart battery charger (off shore power).
Sorry to ramble on. I'll close by mentioning that in my experience, later boats tended to be much more "heavily optioned". Most of those options are nice to have, and are expensive to add.