While doing the dishes I was pondering over it some more.
I still think there are two categories in attributes (not mutually exclusive)
1) Giving information to the potential cacher who found your cache-page
2) Providing information to a search-engine for those caches who have specific wishes.
I hope most people agree with me that geocaching encompasses the Forest Gump principle: Geocaching is like a box of chocolates, you never know what ya gonna get. From this principle, I find that attributes of category 1) should still contain minimal information. Personally, instead of stating 'poisonous plants', I would prefer 'wear covering clothes', and instead of 'ticks' I would also prefer 'wear covering clothes'.
On the other hand, because of 2), the attributes should contain 'often queried information', and therefore state details like 'boat' or 'swim' rather than just 'wet'.
I think the desired level of accuracy for attributes can only be found by letting the number grow in a moderated way, and by looking at what is actually used in cache pages. Furthermore, editing the cache pages can be done in a similar way as with the clickable smileys. Only show the often used and most general attributes in the standard list, and save the more subtle attributes for an extended list that people may refer to if they want.
Finally, it is very important to weigh the value of the symbols and their descriptions. I read in an earlier post that someone equated 'puzzle cache' with 'read the instructions first'. However, my feeling is that 'read the instructions' is MUCH broader, because I would hesitate to call a cach with the requirement to 'state the number of pilars in your log' a puzzle cache. Still it requires you to read the log. IMHO 'read the instructions first' is an icon of category 1), while 'puzzle cache' is an icon of category 2).