I have recently added tag wikis for several games, and loosely based the content on this question. I have added very basic information to help identify the games in question (full name, publisher, year of first release, platforms etc).
I stumbled on this question regarding logos which made me think that maybe (and particular for more obscure games) it would be worth adding a screenshot of the game to the tag wiki. Often pictures can do a lot more than descriptions, and in this case I believe just seeing a single screenshot will help jog your memory about older games.
If I come across a tag with no wiki can I add a single screenshot with a simple description of the game?