Some thoughts…
I think that as with any website that has grown to this level, it is usually better to structure/regulate the data sooner then later - otherwise it progressively gets more harder and restrictive to develop and/or more time consuming to parse the existing data into separate database fields.
For instance, as a user, I might want to look for hikes that don’t have a fee - or perhaps are within my budget. It would be easy to add another field to the search form - but since this information is currently stored along with the directions, maps, other references,etc then it would be near impossible to query the database for just hikes that are free. You could try to parse the string data on the fly, but this would add a significant toll on performance, and unless you can get all users to follow instructions and enter fee/permit data in a consistent pattern (good luck) then coming up with reliable regex/parser rules would be hell.
I think you could add extra fields to the form and still keep it easy to use - but the key would be in the layout, helpful validation error messages, dynamically hiding/showing only relevant fields, auto fill, etc.
You may want to have separate ‘quick add’ and ‘advanced add/edit’ forms.
Another trick I have sometimes found works with novice users is not presenting all the fields all at once - hence ‘wizard’ type forms - with field labels that ask questions - like “How long is the walk” and “Is that one way or return” - as opposed to just “Length” and “One Way/Return”. You can create multi page forms, but there are jQuery plugins that can convert a form into a wizard.
It may take a little more time to develop, but what you could also do is when a person ticks off a walk, determine what data is missing and present a field for that missing data only. You could also limit the number of these fields to 3 or 4. This way you could collect more data without deterring users with excessive data entry.
In any case, not many people will add/edit the walks unless they are enthusiastic about hiking and/or the website as a whole - so those that do may not mind a few extra fields.
I have been a little busy lately, but I am happy to contribute some ideas / a static HTML mockup.